From ebde35478a86776caed68098a83c52a3ad83f9c7 Mon Sep 17 00:00:00 2001
From: ccccjone <144291871+ccccjone@users.noreply.github.com>
Date: Sat, 9 Dec 2023 05:34:47 -0800
Subject: [PATCH 01/15] TST: Add test for large integer result in groupby.prod
 (#56384)

---
 pandas/tests/groupby/test_reductions.py | 24 ++++++++++++++++++++++++
 1 file changed, 24 insertions(+)

diff --git a/pandas/tests/groupby/test_reductions.py b/pandas/tests/groupby/test_reductions.py
index 3e78e728f5ea9..425079f943aba 100644
--- a/pandas/tests/groupby/test_reductions.py
+++ b/pandas/tests/groupby/test_reductions.py
@@ -1057,3 +1057,27 @@ def test_regression_allowlist_methods(op, axis, skipna, sort):
         if sort:
             expected = expected.sort_index(axis=axis)
         tm.assert_frame_equal(result, expected)
+
+
+def test_groupby_prod_with_int64_dtype():
+    # GH#46573
+    data = [
+        [1, 11],
+        [1, 41],
+        [1, 17],
+        [1, 37],
+        [1, 7],
+        [1, 29],
+        [1, 31],
+        [1, 2],
+        [1, 3],
+        [1, 43],
+        [1, 5],
+        [1, 47],
+        [1, 19],
+        [1, 88],
+    ]
+    df = DataFrame(data, columns=["A", "B"], dtype="int64")
+    result = df.groupby(["A"]).prod().reset_index()
+    expected = DataFrame({"A": [1], "B": [180970905912331920]}, dtype="int64")
+    tm.assert_frame_equal(result, expected)

From 536ce302fb4b801b9d6690076b538a5c9c20ac17 Mon Sep 17 00:00:00 2001
From: jbrockmendel <jbrockmendel@gmail.com>
Date: Sat, 9 Dec 2023 10:27:41 -0800
Subject: [PATCH 02/15] DEPR: Series[categorical].replace special-casing
 (#56385)

---
 doc/source/whatsnew/v2.2.0.rst                |  1 +
 pandas/core/arrays/categorical.py             | 13 ++++++
 .../tests/arrays/categorical/test_replace.py  | 28 +++++++++++--
 pandas/tests/copy_view/test_replace.py        | 41 ++++++++++++++++---
 pandas/tests/frame/methods/test_replace.py    | 25 ++++++++---
 pandas/tests/groupby/test_groupby_dropna.py   |  4 +-
 .../tests/io/pytables/test_file_handling.py   | 10 ++++-
 pandas/tests/series/methods/test_replace.py   | 17 ++++++--
 8 files changed, 116 insertions(+), 23 deletions(-)

diff --git a/doc/source/whatsnew/v2.2.0.rst b/doc/source/whatsnew/v2.2.0.rst
index 7a0075ab88a3a..fb91219582b14 100644
--- a/doc/source/whatsnew/v2.2.0.rst
+++ b/doc/source/whatsnew/v2.2.0.rst
@@ -474,6 +474,7 @@ Other Deprecations
 - Deprecated the ``kind`` keyword in :meth:`Series.resample` and :meth:`DataFrame.resample`, explicitly cast the object's ``index`` instead (:issue:`55895`)
 - Deprecated the ``ordinal`` keyword in :class:`PeriodIndex`, use :meth:`PeriodIndex.from_ordinals` instead (:issue:`55960`)
 - Deprecated the ``unit`` keyword in :class:`TimedeltaIndex` construction, use :func:`to_timedelta` instead (:issue:`55499`)
+- Deprecated the behavior of :meth:`DataFrame.replace` and :meth:`Series.replace` with :class:`CategoricalDtype`; in a future version replace will change the values while preserving the categories. To change the categories, use ``ser.cat.rename_categories`` instead (:issue:`55147`)
 - Deprecated the behavior of :meth:`Series.value_counts` and :meth:`Index.value_counts` with object dtype; in a future version these will not perform dtype inference on the resulting :class:`Index`, do ``result.index = result.index.infer_objects()`` to retain the old behavior (:issue:`56161`)
 - Deprecated the default of ``observed=False`` in :meth:`DataFrame.pivot_table`; will be ``True`` in a future version (:issue:`56236`)
 - Deprecated the extension test classes ``BaseNoReduceTests``, ``BaseBooleanReduceTests``, and ``BaseNumericReduceTests``, use ``BaseReduceTests`` instead (:issue:`54663`)
diff --git a/pandas/core/arrays/categorical.py b/pandas/core/arrays/categorical.py
index eec833c600177..f0aabbb863a79 100644
--- a/pandas/core/arrays/categorical.py
+++ b/pandas/core/arrays/categorical.py
@@ -2626,6 +2626,8 @@ def isin(self, values) -> npt.NDArray[np.bool_]:
     def _replace(self, *, to_replace, value, inplace: bool = False):
         from pandas import Index
 
+        orig_dtype = self.dtype
+
         inplace = validate_bool_kwarg(inplace, "inplace")
         cat = self if inplace else self.copy()
 
@@ -2656,6 +2658,17 @@ def _replace(self, *, to_replace, value, inplace: bool = False):
         new_dtype = CategoricalDtype(new_categories, ordered=self.dtype.ordered)
         NDArrayBacked.__init__(cat, new_codes, new_dtype)
 
+        if new_dtype != orig_dtype:
+            warnings.warn(
+                # GH#55147
+                "The behavior of Series.replace (and DataFrame.replace) with "
+                "CategoricalDtype is deprecated. In a future version, replace "
+                "will only be used for cases that preserve the categories. "
+                "To change the categories, use ser.cat.rename_categories "
+                "instead.",
+                FutureWarning,
+                stacklevel=find_stack_level(),
+            )
         if not inplace:
             return cat
 
diff --git a/pandas/tests/arrays/categorical/test_replace.py b/pandas/tests/arrays/categorical/test_replace.py
index 0611d04d36d10..3c677142846d7 100644
--- a/pandas/tests/arrays/categorical/test_replace.py
+++ b/pandas/tests/arrays/categorical/test_replace.py
@@ -31,6 +31,9 @@
         ([1, 2, "3"], "5", ["5", "5", 3], True),
     ],
 )
+@pytest.mark.filterwarnings(
+    "ignore:.*with CategoricalDtype is deprecated:FutureWarning"
+)
 def test_replace_categorical_series(to_replace, value, expected, flip_categories):
     # GH 31720
 
@@ -60,7 +63,13 @@ def test_replace_categorical(to_replace, value, result, expected_error_msg):
     # GH#26988
     cat = Categorical(["a", "b"])
     expected = Categorical(result)
-    result = pd.Series(cat, copy=False).replace(to_replace, value)._values
+    msg = (
+        r"The behavior of Series\.replace \(and DataFrame.replace\) "
+        "with CategoricalDtype"
+    )
+    warn = FutureWarning if expected_error_msg is not None else None
+    with tm.assert_produces_warning(warn, match=msg):
+        result = pd.Series(cat, copy=False).replace(to_replace, value)._values
 
     tm.assert_categorical_equal(result, expected)
     if to_replace == "b":  # the "c" test is supposed to be unchanged
@@ -69,14 +78,20 @@ def test_replace_categorical(to_replace, value, result, expected_error_msg):
             tm.assert_categorical_equal(cat, expected)
 
     ser = pd.Series(cat, copy=False)
-    ser.replace(to_replace, value, inplace=True)
+    with tm.assert_produces_warning(warn, match=msg):
+        ser.replace(to_replace, value, inplace=True)
     tm.assert_categorical_equal(cat, expected)
 
 
 def test_replace_categorical_ea_dtype():
     # GH49404
     cat = Categorical(pd.array(["a", "b"], dtype="string"))
-    result = pd.Series(cat).replace(["a", "b"], ["c", pd.NA])._values
+    msg = (
+        r"The behavior of Series\.replace \(and DataFrame.replace\) "
+        "with CategoricalDtype"
+    )
+    with tm.assert_produces_warning(FutureWarning, match=msg):
+        result = pd.Series(cat).replace(["a", "b"], ["c", pd.NA])._values
     expected = Categorical(pd.array(["c", pd.NA], dtype="string"))
     tm.assert_categorical_equal(result, expected)
 
@@ -85,7 +100,12 @@ def test_replace_maintain_ordering():
     # GH51016
     dtype = pd.CategoricalDtype([0, 1, 2], ordered=True)
     ser = pd.Series([0, 1, 2], dtype=dtype)
-    result = ser.replace(0, 2)
+    msg = (
+        r"The behavior of Series\.replace \(and DataFrame.replace\) "
+        "with CategoricalDtype"
+    )
+    with tm.assert_produces_warning(FutureWarning, match=msg):
+        result = ser.replace(0, 2)
     expected_dtype = pd.CategoricalDtype([1, 2], ordered=True)
     expected = pd.Series([2, 1, 2], dtype=expected_dtype)
     tm.assert_series_equal(expected, result, check_category_order=True)
diff --git a/pandas/tests/copy_view/test_replace.py b/pandas/tests/copy_view/test_replace.py
index 268e859e782ec..6d16bc3083883 100644
--- a/pandas/tests/copy_view/test_replace.py
+++ b/pandas/tests/copy_view/test_replace.py
@@ -162,13 +162,19 @@ def test_replace_to_replace_wrong_dtype(using_copy_on_write):
 def test_replace_list_categorical(using_copy_on_write):
     df = DataFrame({"a": ["a", "b", "c"]}, dtype="category")
     arr = get_array(df, "a")
-    df.replace(["c"], value="a", inplace=True)
+    msg = (
+        r"The behavior of Series\.replace \(and DataFrame.replace\) "
+        "with CategoricalDtype"
+    )
+    with tm.assert_produces_warning(FutureWarning, match=msg):
+        df.replace(["c"], value="a", inplace=True)
     assert np.shares_memory(arr.codes, get_array(df, "a").codes)
     if using_copy_on_write:
         assert df._mgr._has_no_reference(0)
 
     df_orig = df.copy()
-    df2 = df.replace(["b"], value="a")
+    with tm.assert_produces_warning(FutureWarning, match=msg):
+        df2 = df.replace(["b"], value="a")
     assert not np.shares_memory(arr.codes, get_array(df2, "a").codes)
 
     tm.assert_frame_equal(df, df_orig)
@@ -178,7 +184,12 @@ def test_replace_list_inplace_refs_categorical(using_copy_on_write):
     df = DataFrame({"a": ["a", "b", "c"]}, dtype="category")
     view = df[:]
     df_orig = df.copy()
-    df.replace(["c"], value="a", inplace=True)
+    msg = (
+        r"The behavior of Series\.replace \(and DataFrame.replace\) "
+        "with CategoricalDtype"
+    )
+    with tm.assert_produces_warning(FutureWarning, match=msg):
+        df.replace(["c"], value="a", inplace=True)
     if using_copy_on_write:
         assert not np.shares_memory(
             get_array(view, "a").codes, get_array(df, "a").codes
@@ -238,7 +249,13 @@ def test_replace_categorical_inplace_reference(using_copy_on_write, val, to_repl
     df_orig = df.copy()
     arr_a = get_array(df, "a")
     view = df[:]
-    df.replace(to_replace=to_replace, value=val, inplace=True)
+    msg = (
+        r"The behavior of Series\.replace \(and DataFrame.replace\) "
+        "with CategoricalDtype"
+    )
+    warn = FutureWarning if val == 1.5 else None
+    with tm.assert_produces_warning(warn, match=msg):
+        df.replace(to_replace=to_replace, value=val, inplace=True)
 
     if using_copy_on_write:
         assert not np.shares_memory(get_array(df, "a").codes, arr_a.codes)
@@ -253,7 +270,13 @@ def test_replace_categorical_inplace_reference(using_copy_on_write, val, to_repl
 def test_replace_categorical_inplace(using_copy_on_write, val):
     df = DataFrame({"a": Categorical([1, 2, 3])})
     arr_a = get_array(df, "a")
-    df.replace(to_replace=1, value=val, inplace=True)
+    msg = (
+        r"The behavior of Series\.replace \(and DataFrame.replace\) "
+        "with CategoricalDtype"
+    )
+    warn = FutureWarning if val == 1.5 else None
+    with tm.assert_produces_warning(warn, match=msg):
+        df.replace(to_replace=1, value=val, inplace=True)
 
     assert np.shares_memory(get_array(df, "a").codes, arr_a.codes)
     if using_copy_on_write:
@@ -267,7 +290,13 @@ def test_replace_categorical_inplace(using_copy_on_write, val):
 def test_replace_categorical(using_copy_on_write, val):
     df = DataFrame({"a": Categorical([1, 2, 3])})
     df_orig = df.copy()
-    df2 = df.replace(to_replace=1, value=val)
+    msg = (
+        r"The behavior of Series\.replace \(and DataFrame.replace\) "
+        "with CategoricalDtype"
+    )
+    warn = FutureWarning if val == 1.5 else None
+    with tm.assert_produces_warning(warn, match=msg):
+        df2 = df.replace(to_replace=1, value=val)
 
     if using_copy_on_write:
         assert df._mgr._has_no_reference(0)
diff --git a/pandas/tests/frame/methods/test_replace.py b/pandas/tests/frame/methods/test_replace.py
index 13e2c1a249ac2..53c45a5f4b5c6 100644
--- a/pandas/tests/frame/methods/test_replace.py
+++ b/pandas/tests/frame/methods/test_replace.py
@@ -1279,7 +1279,9 @@ def test_categorical_replace_with_dict(self, replace_dict, final_data):
         b = pd.Categorical(final_data[:, 1], categories=ex_cat)
 
         expected = DataFrame({"a": a, "b": b})
-        result = df.replace(replace_dict, 3)
+        msg2 = "with CategoricalDtype is deprecated"
+        with tm.assert_produces_warning(FutureWarning, match=msg2):
+            result = df.replace(replace_dict, 3)
         tm.assert_frame_equal(result, expected)
         msg = (
             r"Attributes of DataFrame.iloc\[:, 0\] \(column name=\"a\"\) are "
@@ -1288,7 +1290,8 @@ def test_categorical_replace_with_dict(self, replace_dict, final_data):
         with pytest.raises(AssertionError, match=msg):
             # ensure non-inplace call does not affect original
             tm.assert_frame_equal(df, expected)
-        return_value = df.replace(replace_dict, 3, inplace=True)
+        with tm.assert_produces_warning(FutureWarning, match=msg2):
+            return_value = df.replace(replace_dict, 3, inplace=True)
         assert return_value is None
         tm.assert_frame_equal(df, expected)
 
@@ -1438,9 +1441,14 @@ def test_replace_value_category_type(self):
         )
 
         # replace values in input dataframe
-        input_df = input_df.replace("d", "z")
-        input_df = input_df.replace("obj1", "obj9")
-        result = input_df.replace("cat2", "catX")
+        msg = (
+            r"The behavior of Series\.replace \(and DataFrame.replace\) "
+            "with CategoricalDtype"
+        )
+        with tm.assert_produces_warning(FutureWarning, match=msg):
+            input_df = input_df.replace("d", "z")
+            input_df = input_df.replace("obj1", "obj9")
+            result = input_df.replace("cat2", "catX")
 
         tm.assert_frame_equal(result, expected)
 
@@ -1466,7 +1474,12 @@ def test_replace_dict_category_type(self):
         )
 
         # replace values in input dataframe using a dict
-        result = input_df.replace({"a": "z", "obj1": "obj9", "cat1": "catX"})
+        msg = (
+            r"The behavior of Series\.replace \(and DataFrame.replace\) "
+            "with CategoricalDtype"
+        )
+        with tm.assert_produces_warning(FutureWarning, match=msg):
+            result = input_df.replace({"a": "z", "obj1": "obj9", "cat1": "catX"})
 
         tm.assert_frame_equal(result, expected)
 
diff --git a/pandas/tests/groupby/test_groupby_dropna.py b/pandas/tests/groupby/test_groupby_dropna.py
index b40c8f45b6d19..4f54621b19b64 100644
--- a/pandas/tests/groupby/test_groupby_dropna.py
+++ b/pandas/tests/groupby/test_groupby_dropna.py
@@ -546,9 +546,9 @@ def test_categorical_reducers(reduction_func, observed, sort, as_index, index_ki
 
     gb_filled = df_filled.groupby(keys, observed=observed, sort=sort, as_index=True)
     expected = getattr(gb_filled, reduction_func)(*args_filled).reset_index()
-    expected["x"] = expected["x"].replace(4, None)
+    expected["x"] = expected["x"].cat.remove_categories([4])
     if index_kind == "multi":
-        expected["x2"] = expected["x2"].replace(4, None)
+        expected["x2"] = expected["x2"].cat.remove_categories([4])
     if as_index:
         if index_kind == "multi":
             expected = expected.set_index(["x", "x2"])
diff --git a/pandas/tests/io/pytables/test_file_handling.py b/pandas/tests/io/pytables/test_file_handling.py
index e292bc7fe251e..d93de16816725 100644
--- a/pandas/tests/io/pytables/test_file_handling.py
+++ b/pandas/tests/io/pytables/test_file_handling.py
@@ -341,7 +341,15 @@ def test_latin_encoding(tmp_path, setup_path, dtype, val):
     ser.to_hdf(store, key=key, format="table", encoding=enc, nan_rep=nan_rep)
     retr = read_hdf(store, key)
 
-    s_nan = ser.replace(nan_rep, np.nan)
+    # TODO:(3.0): once Categorical replace deprecation is enforced,
+    #  we may be able to re-simplify the construction of s_nan
+    if dtype == "category":
+        if nan_rep in ser.cat.categories:
+            s_nan = ser.cat.remove_categories([nan_rep])
+        else:
+            s_nan = ser
+    else:
+        s_nan = ser.replace(nan_rep, np.nan)
 
     tm.assert_series_equal(s_nan, retr)
 
diff --git a/pandas/tests/series/methods/test_replace.py b/pandas/tests/series/methods/test_replace.py
index 477f36bdf4214..4330153c186ca 100644
--- a/pandas/tests/series/methods/test_replace.py
+++ b/pandas/tests/series/methods/test_replace.py
@@ -403,6 +403,7 @@ def test_replace_categorical(self, categorical, numeric):
         # GH 24971, GH#23305
         ser = pd.Series(categorical)
         msg = "Downcasting behavior in `replace`"
+        msg = "with CategoricalDtype is deprecated"
         with tm.assert_produces_warning(FutureWarning, match=msg):
             result = ser.replace({"A": 1, "B": 2})
         expected = pd.Series(numeric).astype("category")
@@ -418,7 +419,9 @@ def test_replace_categorical(self, categorical, numeric):
     def test_replace_categorical_inplace(self, data, data_exp):
         # GH 53358
         result = pd.Series(data, dtype="category")
-        result.replace(to_replace="a", value="b", inplace=True)
+        msg = "with CategoricalDtype is deprecated"
+        with tm.assert_produces_warning(FutureWarning, match=msg):
+            result.replace(to_replace="a", value="b", inplace=True)
         expected = pd.Series(data_exp, dtype="category")
         tm.assert_series_equal(result, expected)
 
@@ -434,16 +437,22 @@ def test_replace_categorical_single(self):
         expected = expected.cat.remove_unused_categories()
         assert c[2] != "foo"
 
-        result = c.replace(c[2], "foo")
+        msg = "with CategoricalDtype is deprecated"
+        with tm.assert_produces_warning(FutureWarning, match=msg):
+            result = c.replace(c[2], "foo")
         tm.assert_series_equal(expected, result)
         assert c[2] != "foo"  # ensure non-inplace call does not alter original
 
-        return_value = c.replace(c[2], "foo", inplace=True)
+        msg = "with CategoricalDtype is deprecated"
+        with tm.assert_produces_warning(FutureWarning, match=msg):
+            return_value = c.replace(c[2], "foo", inplace=True)
         assert return_value is None
         tm.assert_series_equal(expected, c)
 
         first_value = c[0]
-        return_value = c.replace(c[1], c[0], inplace=True)
+        msg = "with CategoricalDtype is deprecated"
+        with tm.assert_produces_warning(FutureWarning, match=msg):
+            return_value = c.replace(c[1], c[0], inplace=True)
         assert return_value is None
         assert c[0] == c[1] == first_value  # test replacing with existing value
 

From 4f8bb2b0ff03b83d8783de0918c336c4ab000327 Mon Sep 17 00:00:00 2001
From: jbrockmendel <jbrockmendel@gmail.com>
Date: Sat, 9 Dec 2023 10:28:36 -0800
Subject: [PATCH 03/15] TST: misplaced tests (#56424)

---
 pandas/tests/io/parser/test_parse_dates.py | 46 ----------------------
 pandas/tests/io/sas/test_sas7bdat.py       | 22 +++++------
 pandas/tests/io/test_feather.py            |  3 +-
 pandas/tests/tslibs/test_parsing.py        | 45 +++++++++++++++++++++
 4 files changed, 57 insertions(+), 59 deletions(-)

diff --git a/pandas/tests/io/parser/test_parse_dates.py b/pandas/tests/io/parser/test_parse_dates.py
index 113402cda1b9a..9355d6089b742 100644
--- a/pandas/tests/io/parser/test_parse_dates.py
+++ b/pandas/tests/io/parser/test_parse_dates.py
@@ -12,13 +12,11 @@
 from io import StringIO
 
 from dateutil.parser import parse as du_parse
-from hypothesis import given
 import numpy as np
 import pytest
 import pytz
 
 from pandas._libs.tslibs import parsing
-from pandas._libs.tslibs.parsing import py_parse_datetime_string
 
 import pandas as pd
 from pandas import (
@@ -30,7 +28,6 @@
     Timestamp,
 )
 import pandas._testing as tm
-from pandas._testing._hypothesis import DATETIME_NO_TZ
 from pandas.core.indexes.datetimes import date_range
 from pandas.core.tools.datetimes import start_caching_at
 
@@ -1838,49 +1835,6 @@ def test_parse_multiple_delimited_dates_with_swap_warnings():
         pd.to_datetime(["01/01/2000", "31/05/2000", "31/05/2001", "01/02/2000"])
 
 
-def _helper_hypothesis_delimited_date(call, date_string, **kwargs):
-    msg, result = None, None
-    try:
-        result = call(date_string, **kwargs)
-    except ValueError as err:
-        msg = str(err)
-    return msg, result
-
-
-@given(DATETIME_NO_TZ)
-@pytest.mark.parametrize("delimiter", list(" -./"))
-@pytest.mark.parametrize("dayfirst", [True, False])
-@pytest.mark.parametrize(
-    "date_format",
-    ["%d %m %Y", "%m %d %Y", "%m %Y", "%Y %m %d", "%y %m %d", "%Y%m%d", "%y%m%d"],
-)
-def test_hypothesis_delimited_date(
-    request, date_format, dayfirst, delimiter, test_datetime
-):
-    if date_format == "%m %Y" and delimiter == ".":
-        request.applymarker(
-            pytest.mark.xfail(
-                reason="parse_datetime_string cannot reliably tell whether "
-                "e.g. %m.%Y is a float or a date"
-            )
-        )
-    date_string = test_datetime.strftime(date_format.replace(" ", delimiter))
-
-    except_out_dateutil, result = _helper_hypothesis_delimited_date(
-        py_parse_datetime_string, date_string, dayfirst=dayfirst
-    )
-    except_in_dateutil, expected = _helper_hypothesis_delimited_date(
-        du_parse,
-        date_string,
-        default=datetime(1, 1, 1),
-        dayfirst=dayfirst,
-        yearfirst=False,
-    )
-
-    assert except_out_dateutil == except_in_dateutil
-    assert result == expected
-
-
 # ArrowKeyError: Column 'fdate1' in include_columns does not exist in CSV file
 @skip_pyarrow
 @pytest.mark.parametrize(
diff --git a/pandas/tests/io/sas/test_sas7bdat.py b/pandas/tests/io/sas/test_sas7bdat.py
index 181405dbfee36..2c4fe10ea97a8 100644
--- a/pandas/tests/io/sas/test_sas7bdat.py
+++ b/pandas/tests/io/sas/test_sas7bdat.py
@@ -41,15 +41,15 @@ def data_test_ix(request, dirpath):
 class TestSAS7BDAT:
     @pytest.mark.slow
     def test_from_file(self, dirpath, data_test_ix):
-        df0, test_ix = data_test_ix
+        expected, test_ix = data_test_ix
         for k in test_ix:
             fname = os.path.join(dirpath, f"test{k}.sas7bdat")
             df = pd.read_sas(fname, encoding="utf-8")
-            tm.assert_frame_equal(df, df0)
+            tm.assert_frame_equal(df, expected)
 
     @pytest.mark.slow
     def test_from_buffer(self, dirpath, data_test_ix):
-        df0, test_ix = data_test_ix
+        expected, test_ix = data_test_ix
         for k in test_ix:
             fname = os.path.join(dirpath, f"test{k}.sas7bdat")
             with open(fname, "rb") as f:
@@ -59,37 +59,37 @@ def test_from_buffer(self, dirpath, data_test_ix):
                 buf, format="sas7bdat", iterator=True, encoding="utf-8"
             ) as rdr:
                 df = rdr.read()
-            tm.assert_frame_equal(df, df0)
+            tm.assert_frame_equal(df, expected)
 
     @pytest.mark.slow
     def test_from_iterator(self, dirpath, data_test_ix):
-        df0, test_ix = data_test_ix
+        expected, test_ix = data_test_ix
         for k in test_ix:
             fname = os.path.join(dirpath, f"test{k}.sas7bdat")
             with pd.read_sas(fname, iterator=True, encoding="utf-8") as rdr:
                 df = rdr.read(2)
-                tm.assert_frame_equal(df, df0.iloc[0:2, :])
+                tm.assert_frame_equal(df, expected.iloc[0:2, :])
                 df = rdr.read(3)
-                tm.assert_frame_equal(df, df0.iloc[2:5, :])
+                tm.assert_frame_equal(df, expected.iloc[2:5, :])
 
     @pytest.mark.slow
     def test_path_pathlib(self, dirpath, data_test_ix):
-        df0, test_ix = data_test_ix
+        expected, test_ix = data_test_ix
         for k in test_ix:
             fname = Path(os.path.join(dirpath, f"test{k}.sas7bdat"))
             df = pd.read_sas(fname, encoding="utf-8")
-            tm.assert_frame_equal(df, df0)
+            tm.assert_frame_equal(df, expected)
 
     @td.skip_if_no("py.path")
     @pytest.mark.slow
     def test_path_localpath(self, dirpath, data_test_ix):
         from py.path import local as LocalPath
 
-        df0, test_ix = data_test_ix
+        expected, test_ix = data_test_ix
         for k in test_ix:
             fname = LocalPath(os.path.join(dirpath, f"test{k}.sas7bdat"))
             df = pd.read_sas(fname, encoding="utf-8")
-            tm.assert_frame_equal(df, df0)
+            tm.assert_frame_equal(df, expected)
 
     @pytest.mark.slow
     @pytest.mark.parametrize("chunksize", (3, 5, 10, 11))
diff --git a/pandas/tests/io/test_feather.py b/pandas/tests/io/test_feather.py
index 572abbf7c48f7..15c5953e79bda 100644
--- a/pandas/tests/io/test_feather.py
+++ b/pandas/tests/io/test_feather.py
@@ -15,7 +15,7 @@
     "ignore:Passing a BlockManager to DataFrame:DeprecationWarning"
 )
 
-pyarrow = pytest.importorskip("pyarrow")
+pa = pytest.importorskip("pyarrow")
 
 
 @pytest.mark.single_cpu
@@ -169,7 +169,6 @@ def test_http_path(self, feather_file, httpserver):
 
     def test_read_feather_dtype_backend(self, string_storage, dtype_backend):
         # GH#50765
-        pa = pytest.importorskip("pyarrow")
         df = pd.DataFrame(
             {
                 "a": pd.Series([1, np.nan, 3], dtype="Int64"),
diff --git a/pandas/tests/tslibs/test_parsing.py b/pandas/tests/tslibs/test_parsing.py
index 425decc14251a..d8f23156bd4d4 100644
--- a/pandas/tests/tslibs/test_parsing.py
+++ b/pandas/tests/tslibs/test_parsing.py
@@ -6,6 +6,7 @@
 
 from dateutil.parser import parse as du_parse
 from dateutil.tz import tzlocal
+from hypothesis import given
 import numpy as np
 import pytest
 
@@ -21,6 +22,7 @@
 import pandas.util._test_decorators as td
 
 import pandas._testing as tm
+from pandas._testing._hypothesis import DATETIME_NO_TZ
 
 
 @pytest.mark.skipif(
@@ -367,3 +369,46 @@ def test_guess_datetime_format_f(input):
     result = parsing.guess_datetime_format(input)
     expected = "%Y-%m-%dT%H:%M:%S.%f"
     assert result == expected
+
+
+def _helper_hypothesis_delimited_date(call, date_string, **kwargs):
+    msg, result = None, None
+    try:
+        result = call(date_string, **kwargs)
+    except ValueError as err:
+        msg = str(err)
+    return msg, result
+
+
+@given(DATETIME_NO_TZ)
+@pytest.mark.parametrize("delimiter", list(" -./"))
+@pytest.mark.parametrize("dayfirst", [True, False])
+@pytest.mark.parametrize(
+    "date_format",
+    ["%d %m %Y", "%m %d %Y", "%m %Y", "%Y %m %d", "%y %m %d", "%Y%m%d", "%y%m%d"],
+)
+def test_hypothesis_delimited_date(
+    request, date_format, dayfirst, delimiter, test_datetime
+):
+    if date_format == "%m %Y" and delimiter == ".":
+        request.applymarker(
+            pytest.mark.xfail(
+                reason="parse_datetime_string cannot reliably tell whether "
+                "e.g. %m.%Y is a float or a date"
+            )
+        )
+    date_string = test_datetime.strftime(date_format.replace(" ", delimiter))
+
+    except_out_dateutil, result = _helper_hypothesis_delimited_date(
+        parsing.py_parse_datetime_string, date_string, dayfirst=dayfirst
+    )
+    except_in_dateutil, expected = _helper_hypothesis_delimited_date(
+        du_parse,
+        date_string,
+        default=datetime(1, 1, 1),
+        dayfirst=dayfirst,
+        yearfirst=False,
+    )
+
+    assert except_out_dateutil == except_in_dateutil
+    assert result == expected

From 2dcb963b6ab609b864cd5214478f272783bdf4f8 Mon Sep 17 00:00:00 2001
From: jbrockmendel <jbrockmendel@gmail.com>
Date: Sat, 9 Dec 2023 10:29:50 -0800
Subject: [PATCH 04/15] TYP: EA.isin (#56423)

---
 pandas/core/arrays/arrow/array.py  |  2 +-
 pandas/core/arrays/base.py         |  4 ++--
 pandas/core/arrays/categorical.py  | 11 ++---------
 pandas/core/arrays/datetimelike.py | 20 ++++++++++++--------
 pandas/core/arrays/interval.py     |  8 ++------
 pandas/core/arrays/masked.py       |  2 +-
 pandas/core/arrays/string_arrow.py |  3 ++-
 7 files changed, 22 insertions(+), 28 deletions(-)

diff --git a/pandas/core/arrays/arrow/array.py b/pandas/core/arrays/arrow/array.py
index 5abdfe69e52c0..d8b074fe61322 100644
--- a/pandas/core/arrays/arrow/array.py
+++ b/pandas/core/arrays/arrow/array.py
@@ -1023,7 +1023,7 @@ def fillna(
 
         return super().fillna(value=value, method=method, limit=limit, copy=copy)
 
-    def isin(self, values) -> npt.NDArray[np.bool_]:
+    def isin(self, values: ArrayLike) -> npt.NDArray[np.bool_]:
         # short-circuit to return all False array.
         if not len(values):
             return np.zeros(len(self), dtype=bool)
diff --git a/pandas/core/arrays/base.py b/pandas/core/arrays/base.py
index e61e374009163..3272a594f4cf4 100644
--- a/pandas/core/arrays/base.py
+++ b/pandas/core/arrays/base.py
@@ -1355,7 +1355,7 @@ def equals(self, other: object) -> bool:
             equal_na = self.isna() & other.isna()  # type: ignore[operator]
             return bool((equal_values | equal_na).all())
 
-    def isin(self, values) -> npt.NDArray[np.bool_]:
+    def isin(self, values: ArrayLike) -> npt.NDArray[np.bool_]:
         """
         Pointwise comparison for set containment in the given values.
 
@@ -1363,7 +1363,7 @@ def isin(self, values) -> npt.NDArray[np.bool_]:
 
         Parameters
         ----------
-        values : Sequence
+        values : np.ndarray or ExtensionArray
 
         Returns
         -------
diff --git a/pandas/core/arrays/categorical.py b/pandas/core/arrays/categorical.py
index f0aabbb863a79..20aec52b606b6 100644
--- a/pandas/core/arrays/categorical.py
+++ b/pandas/core/arrays/categorical.py
@@ -2570,7 +2570,7 @@ def describe(self) -> DataFrame:
 
         return result
 
-    def isin(self, values) -> npt.NDArray[np.bool_]:
+    def isin(self, values: ArrayLike) -> npt.NDArray[np.bool_]:
         """
         Check whether `values` are contained in Categorical.
 
@@ -2580,7 +2580,7 @@ def isin(self, values) -> npt.NDArray[np.bool_]:
 
         Parameters
         ----------
-        values : set or list-like
+        values : np.ndarray or ExtensionArray
             The sequence of values to test. Passing in a single string will
             raise a ``TypeError``. Instead, turn a single string into a
             list of one element.
@@ -2611,13 +2611,6 @@ def isin(self, values) -> npt.NDArray[np.bool_]:
         >>> s.isin(['lama'])
         array([ True, False,  True, False,  True, False])
         """
-        if not is_list_like(values):
-            values_type = type(values).__name__
-            raise TypeError(
-                "only list-like objects are allowed to be passed "
-                f"to isin(), you passed a `{values_type}`"
-            )
-        values = sanitize_array(values, None, None)
         null_mask = np.asarray(isna(values))
         code_values = self.categories.get_indexer_for(values)
         code_values = code_values[null_mask | (code_values >= 0)]
diff --git a/pandas/core/arrays/datetimelike.py b/pandas/core/arrays/datetimelike.py
index eb1c2ecc0b0fe..2a6a45ad18421 100644
--- a/pandas/core/arrays/datetimelike.py
+++ b/pandas/core/arrays/datetimelike.py
@@ -734,22 +734,19 @@ def map(self, mapper, na_action=None):
         else:
             return result.array
 
-    def isin(self, values) -> npt.NDArray[np.bool_]:
+    def isin(self, values: ArrayLike) -> npt.NDArray[np.bool_]:
         """
         Compute boolean array of whether each value is found in the
         passed set of values.
 
         Parameters
         ----------
-        values : set or sequence of values
+        values : np.ndarray or ExtensionArray
 
         Returns
         -------
         ndarray[bool]
         """
-        if not hasattr(values, "dtype"):
-            values = np.asarray(values)
-
         if values.dtype.kind in "fiuc":
             # TODO: de-duplicate with equals, validate_comparison_value
             return np.zeros(self.shape, dtype=bool)
@@ -781,15 +778,22 @@ def isin(self, values) -> npt.NDArray[np.bool_]:
 
         if self.dtype.kind in "mM":
             self = cast("DatetimeArray | TimedeltaArray", self)
-            values = values.as_unit(self.unit)
+            # error: Item "ExtensionArray" of "ExtensionArray | ndarray[Any, Any]"
+            # has no attribute "as_unit"
+            values = values.as_unit(self.unit)  # type: ignore[union-attr]
 
         try:
-            self._check_compatible_with(values)
+            # error: Argument 1 to "_check_compatible_with" of "DatetimeLikeArrayMixin"
+            # has incompatible type "ExtensionArray | ndarray[Any, Any]"; expected
+            # "Period | Timestamp | Timedelta | NaTType"
+            self._check_compatible_with(values)  # type: ignore[arg-type]
         except (TypeError, ValueError):
             # Includes tzawareness mismatch and IncompatibleFrequencyError
             return np.zeros(self.shape, dtype=bool)
 
-        return isin(self.asi8, values.asi8)
+        # error: Item "ExtensionArray" of "ExtensionArray | ndarray[Any, Any]"
+        # has no attribute "asi8"
+        return isin(self.asi8, values.asi8)  # type: ignore[union-attr]
 
     # ------------------------------------------------------------------
     # Null Handling
diff --git a/pandas/core/arrays/interval.py b/pandas/core/arrays/interval.py
index 126484ed4a2a0..383f8a49fd02c 100644
--- a/pandas/core/arrays/interval.py
+++ b/pandas/core/arrays/interval.py
@@ -1789,12 +1789,8 @@ def contains(self, other):
             other < self._right if self.open_right else other <= self._right
         )
 
-    def isin(self, values) -> npt.NDArray[np.bool_]:
-        if not hasattr(values, "dtype"):
-            values = np.array(values)
-        values = extract_array(values, extract_numpy=True)
-
-        if isinstance(values.dtype, IntervalDtype):
+    def isin(self, values: ArrayLike) -> npt.NDArray[np.bool_]:
+        if isinstance(values, IntervalArray):
             if self.closed != values.closed:
                 # not comparable -> no overlap
                 return np.zeros(self.shape, dtype=bool)
diff --git a/pandas/core/arrays/masked.py b/pandas/core/arrays/masked.py
index 201ce44ed0163..2f0cf7a67c1cc 100644
--- a/pandas/core/arrays/masked.py
+++ b/pandas/core/arrays/masked.py
@@ -955,7 +955,7 @@ def take(
 
     # error: Return type "BooleanArray" of "isin" incompatible with return type
     # "ndarray" in supertype "ExtensionArray"
-    def isin(self, values) -> BooleanArray:  # type: ignore[override]
+    def isin(self, values: ArrayLike) -> BooleanArray:  # type: ignore[override]
         from pandas.core.arrays import BooleanArray
 
         # algorithms.isin will eventually convert values to an ndarray, so no extra
diff --git a/pandas/core/arrays/string_arrow.py b/pandas/core/arrays/string_arrow.py
index 976a8d3c32b23..21fe7cd8180ad 100644
--- a/pandas/core/arrays/string_arrow.py
+++ b/pandas/core/arrays/string_arrow.py
@@ -54,6 +54,7 @@
     from collections.abc import Sequence
 
     from pandas._typing import (
+        ArrayLike,
         AxisInt,
         Dtype,
         Scalar,
@@ -212,7 +213,7 @@ def _maybe_convert_setitem_value(self, value):
                     raise TypeError("Scalar must be NA or str")
         return super()._maybe_convert_setitem_value(value)
 
-    def isin(self, values) -> npt.NDArray[np.bool_]:
+    def isin(self, values: ArrayLike) -> npt.NDArray[np.bool_]:
         value_set = [
             pa_scalar.as_py()
             for pa_scalar in [pa.scalar(value, from_pandas=True) for value in values]

From d95a7a79fd9626b46c29509860893954e2889638 Mon Sep 17 00:00:00 2001
From: jbrockmendel <jbrockmendel@gmail.com>
Date: Sat, 9 Dec 2023 10:32:18 -0800
Subject: [PATCH 05/15] DEPR: casting in datetimelike isin (#56427)

* DEPR: casting in datetimelike isin

* GH ref

* update doctest
---
 doc/source/whatsnew/v2.2.0.rst     |  2 ++
 pandas/_libs/lib.pyx               |  7 ++++--
 pandas/core/arrays/datetimelike.py | 21 ++++++++++++++++
 pandas/core/indexes/base.py        | 12 ---------
 pandas/tests/test_algos.py         | 39 ++++++++++++++++++++++++++++++
 5 files changed, 67 insertions(+), 14 deletions(-)

diff --git a/doc/source/whatsnew/v2.2.0.rst b/doc/source/whatsnew/v2.2.0.rst
index fb91219582b14..e51a347dec46c 100644
--- a/doc/source/whatsnew/v2.2.0.rst
+++ b/doc/source/whatsnew/v2.2.0.rst
@@ -455,6 +455,7 @@ Other Deprecations
 - Deprecated allowing non-keyword arguments in :meth:`DataFrame.to_xml` except ``path_or_buffer``. (:issue:`54229`)
 - Deprecated allowing passing :class:`BlockManager` objects to :class:`DataFrame` or :class:`SingleBlockManager` objects to :class:`Series` (:issue:`52419`)
 - Deprecated behavior of :meth:`Index.insert` with an object-dtype index silently performing type inference on the result, explicitly call ``result.infer_objects(copy=False)`` for the old behavior instead (:issue:`51363`)
+- Deprecated casting non-datetimelike values (mainly strings) in :meth:`Series.isin` and :meth:`Index.isin` with ``datetime64``, ``timedelta64``, and :class:`PeriodDtype` dtypes (:issue:`53111`)
 - Deprecated downcasting behavior in :meth:`Series.where`, :meth:`DataFrame.where`, :meth:`Series.mask`, :meth:`DataFrame.mask`, :meth:`Series.clip`, :meth:`DataFrame.clip`; in a future version these will not infer object-dtype columns to non-object dtype, or all-round floats to integer dtype. Call ``result.infer_objects(copy=False)`` on the result for object inference, or explicitly cast floats to ints. To opt in to the future version, use ``pd.set_option("future.no_silent_downcasting", True)`` (:issue:`53656`)
 - Deprecated including the groups in computations when using :meth:`.DataFrameGroupBy.apply` and :meth:`.DataFrameGroupBy.resample`; pass ``include_groups=False`` to exclude the groups (:issue:`7155`)
 - Deprecated indexing an :class:`Index`  with a boolean indexer of length zero (:issue:`55820`)
@@ -526,6 +527,7 @@ Datetimelike
 ^^^^^^^^^^^^
 - Bug in :class:`DatetimeIndex` construction when passing both a ``tz`` and either ``dayfirst`` or ``yearfirst`` ignoring dayfirst/yearfirst (:issue:`55813`)
 - Bug in :class:`DatetimeIndex` when passing an object-dtype ndarray of float objects and a ``tz`` incorrectly localizing the result (:issue:`55780`)
+- Bug in :func:`Series.isin` with :class:`DatetimeTZDtype` dtype and comparison values that are all ``NaT`` incorrectly returning all-``False`` even if the series contains ``NaT`` entries (:issue:`56427`)
 - Bug in :func:`concat` raising ``AttributeError`` when concatenating all-NA DataFrame with :class:`DatetimeTZDtype` dtype DataFrame. (:issue:`52093`)
 - Bug in :func:`testing.assert_extension_array_equal` that could use the wrong unit when comparing resolutions (:issue:`55730`)
 - Bug in :func:`to_datetime` and :class:`DatetimeIndex` when passing a list of mixed-string-and-numeric types incorrectly raising (:issue:`55780`)
diff --git a/pandas/_libs/lib.pyx b/pandas/_libs/lib.pyx
index 8493f8bd066e0..c483f35513a40 100644
--- a/pandas/_libs/lib.pyx
+++ b/pandas/_libs/lib.pyx
@@ -2756,8 +2756,11 @@ def maybe_convert_objects(ndarray[object] objects,
                     res[:] = NPY_NAT
                     return res
             elif dtype is not None:
-                # EA, we don't expect to get here, but _could_ implement
-                raise NotImplementedError(dtype)
+                # i.e. PeriodDtype, DatetimeTZDtype
+                cls = dtype.construct_array_type()
+                obj = cls._from_sequence([], dtype=dtype)
+                taker = -np.ones((<object>objects).shape, dtype=np.intp)
+                return obj.take(taker, allow_fill=True)
             else:
                 # we don't guess
                 seen.object_ = True
diff --git a/pandas/core/arrays/datetimelike.py b/pandas/core/arrays/datetimelike.py
index 2a6a45ad18421..3249f432e22a9 100644
--- a/pandas/core/arrays/datetimelike.py
+++ b/pandas/core/arrays/datetimelike.py
@@ -751,6 +751,8 @@ def isin(self, values: ArrayLike) -> npt.NDArray[np.bool_]:
             # TODO: de-duplicate with equals, validate_comparison_value
             return np.zeros(self.shape, dtype=bool)
 
+        values = ensure_wrapped_if_datetimelike(values)
+
         if not isinstance(values, type(self)):
             inferable = [
                 "timedelta",
@@ -761,6 +763,14 @@ def isin(self, values: ArrayLike) -> npt.NDArray[np.bool_]:
                 "period",
             ]
             if values.dtype == object:
+                values = lib.maybe_convert_objects(
+                    values,
+                    convert_non_numeric=True,
+                    dtype_if_all_nat=self.dtype,
+                )
+                if values.dtype != object:
+                    return self.isin(values)
+
                 inferred = lib.infer_dtype(values, skipna=False)
                 if inferred not in inferable:
                     if inferred == "string":
@@ -775,6 +785,17 @@ def isin(self, values: ArrayLike) -> npt.NDArray[np.bool_]:
                 values = type(self)._from_sequence(values)
             except ValueError:
                 return isin(self.astype(object), values)
+            else:
+                warnings.warn(
+                    # GH#53111
+                    f"The behavior of 'isin' with dtype={self.dtype} and "
+                    "castable values (e.g. strings) is deprecated. In a "
+                    "future version, these will not be considered matching "
+                    "by isin. Explicitly cast to the appropriate dtype before "
+                    "calling isin instead.",
+                    FutureWarning,
+                    stacklevel=find_stack_level(),
+                )
 
         if self.dtype.kind in "mM":
             self = cast("DatetimeArray | TimedeltaArray", self)
diff --git a/pandas/core/indexes/base.py b/pandas/core/indexes/base.py
index 3d3056f47f15e..febceeb7623b5 100644
--- a/pandas/core/indexes/base.py
+++ b/pandas/core/indexes/base.py
@@ -6534,18 +6534,6 @@ def isin(self, values, level=None) -> npt.NDArray[np.bool_]:
 
         >>> midx.isin([(1, 'red'), (3, 'red')])
         array([ True, False, False])
-
-        For a DatetimeIndex, string values in `values` are converted to
-        Timestamps.
-
-        >>> dates = ['2000-03-11', '2000-03-12', '2000-03-13']
-        >>> dti = pd.to_datetime(dates)
-        >>> dti
-        DatetimeIndex(['2000-03-11', '2000-03-12', '2000-03-13'],
-        dtype='datetime64[ns]', freq=None)
-
-        >>> dti.isin(['2000-03-11'])
-        array([ True, False, False])
         """
         if level is not None:
             self._validate_index_level(level)
diff --git a/pandas/tests/test_algos.py b/pandas/tests/test_algos.py
index 5356704cc64a2..d9162c428b492 100644
--- a/pandas/tests/test_algos.py
+++ b/pandas/tests/test_algos.py
@@ -992,6 +992,45 @@ def test_large(self):
         expected[1] = True
         tm.assert_numpy_array_equal(result, expected)
 
+    @pytest.mark.parametrize("dtype", ["m8[ns]", "M8[ns]", "M8[ns, UTC]", "period[D]"])
+    def test_isin_datetimelike_all_nat(self, dtype):
+        # GH#56427
+        dta = date_range("2013-01-01", periods=3)._values
+        arr = Series(dta.view("i8")).array.view(dtype)
+
+        arr[0] = NaT
+        result = algos.isin(arr, [NaT])
+        expected = np.array([True, False, False], dtype=bool)
+        tm.assert_numpy_array_equal(result, expected)
+
+    @pytest.mark.parametrize("dtype", ["m8[ns]", "M8[ns]", "M8[ns, UTC]"])
+    def test_isin_datetimelike_strings_deprecated(self, dtype):
+        # GH#53111
+        dta = date_range("2013-01-01", periods=3)._values
+        arr = Series(dta.view("i8")).array.view(dtype)
+
+        vals = [str(x) for x in arr]
+        msg = "The behavior of 'isin' with dtype=.* is deprecated"
+        with tm.assert_produces_warning(FutureWarning, match=msg):
+            res = algos.isin(arr, vals)
+        assert res.all()
+
+        vals2 = np.array(vals, dtype=str)
+        with tm.assert_produces_warning(FutureWarning, match=msg):
+            res2 = algos.isin(arr, vals2)
+        assert res2.all()
+
+    def test_isin_dt64tz_with_nat(self):
+        # the all-NaT values used to get inferred to tznaive, which was evaluated
+        #  as non-matching GH#56427
+        dti = date_range("2016-01-01", periods=3, tz="UTC")
+        ser = Series(dti)
+        ser[0] = NaT
+
+        res = algos.isin(ser._values, [NaT])
+        exp = np.array([True, False, False], dtype=bool)
+        tm.assert_numpy_array_equal(res, exp)
+
     def test_categorical_from_codes(self):
         # GH 16639
         vals = np.array([0, 1, 2, 0])

From a6c0ae48fe4da5ee6356e8370f0b401be0f16b1a Mon Sep 17 00:00:00 2001
From: jbrockmendel <jbrockmendel@gmail.com>
Date: Sat, 9 Dec 2023 10:36:28 -0800
Subject: [PATCH 06/15] PERF: datetimelike addition (#56373)

* PERF: datetimelike addition

* re-add import

* remove no-longer-used

* mypy fixup

* troubleshoot 32bit builds
---
 asv_bench/benchmarks/arithmetic.py  | 37 ------------
 pandas/_libs/tslibs/__init__.py     |  2 +
 pandas/_libs/tslibs/np_datetime.pxd |  2 +
 pandas/_libs/tslibs/np_datetime.pyi |  4 ++
 pandas/_libs/tslibs/np_datetime.pyx | 41 +++++++++++++
 pandas/core/algorithms.py           | 92 -----------------------------
 pandas/core/arrays/datetimelike.py  | 20 ++-----
 pandas/core/arrays/period.py        | 11 +---
 pandas/tests/test_algos.py          | 51 ----------------
 pandas/tests/tslibs/test_api.py     |  1 +
 10 files changed, 59 insertions(+), 202 deletions(-)

diff --git a/asv_bench/benchmarks/arithmetic.py b/asv_bench/benchmarks/arithmetic.py
index 5e23cba2e1074..6b1f75187f887 100644
--- a/asv_bench/benchmarks/arithmetic.py
+++ b/asv_bench/benchmarks/arithmetic.py
@@ -12,7 +12,6 @@
     date_range,
     to_timedelta,
 )
-from pandas.core.algorithms import checked_add_with_arr
 
 from .pandas_vb_common import numeric_dtypes
 
@@ -389,42 +388,6 @@ def time_add_timedeltas(self, df):
         df["timedelta"] + df["timedelta"]
 
 
-class AddOverflowScalar:
-    params = [1, -1, 0]
-    param_names = ["scalar"]
-
-    def setup(self, scalar):
-        N = 10**6
-        self.arr = np.arange(N)
-
-    def time_add_overflow_scalar(self, scalar):
-        checked_add_with_arr(self.arr, scalar)
-
-
-class AddOverflowArray:
-    def setup(self):
-        N = 10**6
-        self.arr = np.arange(N)
-        self.arr_rev = np.arange(-N, 0)
-        self.arr_mixed = np.array([1, -1]).repeat(N / 2)
-        self.arr_nan_1 = np.random.choice([True, False], size=N)
-        self.arr_nan_2 = np.random.choice([True, False], size=N)
-
-    def time_add_overflow_arr_rev(self):
-        checked_add_with_arr(self.arr, self.arr_rev)
-
-    def time_add_overflow_arr_mask_nan(self):
-        checked_add_with_arr(self.arr, self.arr_mixed, arr_mask=self.arr_nan_1)
-
-    def time_add_overflow_b_mask_nan(self):
-        checked_add_with_arr(self.arr, self.arr_mixed, b_mask=self.arr_nan_1)
-
-    def time_add_overflow_both_arg_nan(self):
-        checked_add_with_arr(
-            self.arr, self.arr_mixed, arr_mask=self.arr_nan_1, b_mask=self.arr_nan_2
-        )
-
-
 hcal = pd.tseries.holiday.USFederalHolidayCalendar()
 # These offsets currently raise a NotImplementedError with .apply_index()
 non_apply = [
diff --git a/pandas/_libs/tslibs/__init__.py b/pandas/_libs/tslibs/__init__.py
index c622121578dcb..b626959203295 100644
--- a/pandas/_libs/tslibs/__init__.py
+++ b/pandas/_libs/tslibs/__init__.py
@@ -34,6 +34,7 @@
     "npy_unit_to_abbrev",
     "get_supported_reso",
     "guess_datetime_format",
+    "add_overflowsafe",
 ]
 
 from pandas._libs.tslibs import dtypes  # pylint: disable=import-self
@@ -55,6 +56,7 @@
 from pandas._libs.tslibs.np_datetime import (
     OutOfBoundsDatetime,
     OutOfBoundsTimedelta,
+    add_overflowsafe,
     astype_overflowsafe,
     is_unitless,
     py_get_unit_from_dtype as get_unit_from_dtype,
diff --git a/pandas/_libs/tslibs/np_datetime.pxd b/pandas/_libs/tslibs/np_datetime.pxd
index a87c3d3f0955d..cb2658d343772 100644
--- a/pandas/_libs/tslibs/np_datetime.pxd
+++ b/pandas/_libs/tslibs/np_datetime.pxd
@@ -118,3 +118,5 @@ cdef int64_t convert_reso(
     NPY_DATETIMEUNIT to_reso,
     bint round_ok,
 ) except? -1
+
+cpdef cnp.ndarray add_overflowsafe(cnp.ndarray left, cnp.ndarray right)
diff --git a/pandas/_libs/tslibs/np_datetime.pyi b/pandas/_libs/tslibs/np_datetime.pyi
index c42bc43ac9d89..5a4ba673dbeff 100644
--- a/pandas/_libs/tslibs/np_datetime.pyi
+++ b/pandas/_libs/tslibs/np_datetime.pyi
@@ -19,3 +19,7 @@ def is_unitless(dtype: np.dtype) -> bool: ...
 def compare_mismatched_resolutions(
     left: np.ndarray, right: np.ndarray, op
 ) -> npt.NDArray[np.bool_]: ...
+def add_overflowsafe(
+    left: npt.NDArray[np.int64],
+    right: npt.NDArray[np.int64],
+) -> npt.NDArray[np.int64]: ...
diff --git a/pandas/_libs/tslibs/np_datetime.pyx b/pandas/_libs/tslibs/np_datetime.pyx
index 9958206c51b7a..5f5e75b1e64d0 100644
--- a/pandas/_libs/tslibs/np_datetime.pyx
+++ b/pandas/_libs/tslibs/np_datetime.pyx
@@ -1,3 +1,4 @@
+cimport cython
 from cpython.datetime cimport (
     PyDateTime_CheckExact,
     PyDateTime_DATE_GET_HOUR,
@@ -678,3 +679,43 @@ cdef int64_t _convert_reso_with_dtstruct(
         raise OutOfBoundsDatetime from err
 
     return result
+
+
+@cython.overflowcheck(True)
+cpdef cnp.ndarray add_overflowsafe(cnp.ndarray left, cnp.ndarray right):
+    """
+    Overflow-safe addition for datetime64/timedelta64 dtypes.
+
+    `right` may either be zero-dim or of the same shape as `left`.
+    """
+    cdef:
+        Py_ssize_t N = left.size
+        int64_t lval, rval, res_value
+        ndarray iresult = cnp.PyArray_EMPTY(
+            left.ndim, left.shape, cnp.NPY_INT64, 0
+        )
+        cnp.broadcast mi = cnp.PyArray_MultiIterNew3(iresult, left, right)
+
+    # Note: doing this try/except outside the loop improves performance over
+    #  doing it inside the loop.
+    try:
+        for i in range(N):
+            # Analogous to: lval = lvalues[i]
+            lval = (<int64_t*>cnp.PyArray_MultiIter_DATA(mi, 1))[0]
+
+            # Analogous to: rval = rvalues[i]
+            rval = (<int64_t*>cnp.PyArray_MultiIter_DATA(mi, 2))[0]
+
+            if lval == NPY_DATETIME_NAT or rval == NPY_DATETIME_NAT:
+                res_value = NPY_DATETIME_NAT
+            else:
+                res_value = lval + rval
+
+            # Analogous to: result[i] = res_value
+            (<int64_t*>cnp.PyArray_MultiIter_DATA(mi, 0))[0] = res_value
+
+            cnp.PyArray_MultiIter_NEXT(mi)
+    except OverflowError as err:
+        raise OverflowError("Overflow in int64 addition") from err
+
+    return iresult
diff --git a/pandas/core/algorithms.py b/pandas/core/algorithms.py
index 82de8ae96160f..03f06da5f84e1 100644
--- a/pandas/core/algorithms.py
+++ b/pandas/core/algorithms.py
@@ -1119,98 +1119,6 @@ def rank(
     return ranks
 
 
-def checked_add_with_arr(
-    arr: npt.NDArray[np.int64],
-    b: int | npt.NDArray[np.int64],
-    arr_mask: npt.NDArray[np.bool_] | None = None,
-    b_mask: npt.NDArray[np.bool_] | None = None,
-) -> npt.NDArray[np.int64]:
-    """
-    Perform array addition that checks for underflow and overflow.
-
-    Performs the addition of an int64 array and an int64 integer (or array)
-    but checks that they do not result in overflow first. For elements that
-    are indicated to be NaN, whether or not there is overflow for that element
-    is automatically ignored.
-
-    Parameters
-    ----------
-    arr : np.ndarray[int64] addend.
-    b : array or scalar addend.
-    arr_mask : np.ndarray[bool] or None, default None
-        array indicating which elements to exclude from checking
-    b_mask : np.ndarray[bool] or None, default None
-        array or scalar indicating which element(s) to exclude from checking
-
-    Returns
-    -------
-    sum : An array for elements x + b for each element x in arr if b is
-          a scalar or an array for elements x + y for each element pair
-          (x, y) in (arr, b).
-
-    Raises
-    ------
-    OverflowError if any x + y exceeds the maximum or minimum int64 value.
-    """
-    # For performance reasons, we broadcast 'b' to the new array 'b2'
-    # so that it has the same size as 'arr'.
-    b2 = np.broadcast_to(b, arr.shape)
-    if b_mask is not None:
-        # We do the same broadcasting for b_mask as well.
-        b2_mask = np.broadcast_to(b_mask, arr.shape)
-    else:
-        b2_mask = None
-
-    # For elements that are NaN, regardless of their value, we should
-    # ignore whether they overflow or not when doing the checked add.
-    if arr_mask is not None and b2_mask is not None:
-        not_nan = np.logical_not(arr_mask | b2_mask)
-    elif arr_mask is not None:
-        not_nan = np.logical_not(arr_mask)
-    elif b_mask is not None:
-        # error: Argument 1 to "__call__" of "_UFunc_Nin1_Nout1" has
-        # incompatible type "Optional[ndarray[Any, dtype[bool_]]]";
-        # expected "Union[_SupportsArray[dtype[Any]], _NestedSequence
-        # [_SupportsArray[dtype[Any]]], bool, int, float, complex, str
-        # , bytes, _NestedSequence[Union[bool, int, float, complex, str
-        # , bytes]]]"
-        not_nan = np.logical_not(b2_mask)  # type: ignore[arg-type]
-    else:
-        not_nan = np.empty(arr.shape, dtype=bool)
-        not_nan.fill(True)
-
-    # gh-14324: For each element in 'arr' and its corresponding element
-    # in 'b2', we check the sign of the element in 'b2'. If it is positive,
-    # we then check whether its sum with the element in 'arr' exceeds
-    # np.iinfo(np.int64).max. If so, we have an overflow error. If it
-    # it is negative, we then check whether its sum with the element in
-    # 'arr' exceeds np.iinfo(np.int64).min. If so, we have an overflow
-    # error as well.
-    i8max = lib.i8max
-    i8min = iNaT
-
-    mask1 = b2 > 0
-    mask2 = b2 < 0
-
-    if not mask1.any():
-        to_raise = ((i8min - b2 > arr) & not_nan).any()
-    elif not mask2.any():
-        to_raise = ((i8max - b2 < arr) & not_nan).any()
-    else:
-        to_raise = ((i8max - b2[mask1] < arr[mask1]) & not_nan[mask1]).any() or (
-            (i8min - b2[mask2] > arr[mask2]) & not_nan[mask2]
-        ).any()
-
-    if to_raise:
-        raise OverflowError("Overflow in int64 addition")
-
-    result = arr + b
-    if arr_mask is not None or b2_mask is not None:
-        np.putmask(result, ~not_nan, iNaT)
-
-    return result
-
-
 # ---- #
 # take #
 # ---- #
diff --git a/pandas/core/arrays/datetimelike.py b/pandas/core/arrays/datetimelike.py
index 3249f432e22a9..879f477106ae9 100644
--- a/pandas/core/arrays/datetimelike.py
+++ b/pandas/core/arrays/datetimelike.py
@@ -35,6 +35,7 @@
     Tick,
     Timedelta,
     Timestamp,
+    add_overflowsafe,
     astype_overflowsafe,
     get_unit_from_dtype,
     iNaT,
@@ -112,7 +113,6 @@
     ops,
 )
 from pandas.core.algorithms import (
-    checked_add_with_arr,
     isin,
     map_array,
     unique1d,
@@ -1038,7 +1038,7 @@ def _get_i8_values_and_mask(
         self, other
     ) -> tuple[int | npt.NDArray[np.int64], None | npt.NDArray[np.bool_]]:
         """
-        Get the int64 values and b_mask to pass to checked_add_with_arr.
+        Get the int64 values and b_mask to pass to add_overflowsafe.
         """
         if isinstance(other, Period):
             i8values = other.ordinal
@@ -1094,9 +1094,7 @@ def _add_datetimelike_scalar(self, other) -> DatetimeArray:
         self = cast("TimedeltaArray", self)
 
         other_i8, o_mask = self._get_i8_values_and_mask(other)
-        result = checked_add_with_arr(
-            self.asi8, other_i8, arr_mask=self._isnan, b_mask=o_mask
-        )
+        result = add_overflowsafe(self.asi8, np.asarray(other_i8, dtype="i8"))
         res_values = result.view(f"M8[{self.unit}]")
 
         dtype = tz_to_dtype(tz=other.tz, unit=self.unit)
@@ -1159,9 +1157,7 @@ def _sub_datetimelike(self, other: Timestamp | DatetimeArray) -> TimedeltaArray:
             raise type(err)(new_message) from err
 
         other_i8, o_mask = self._get_i8_values_and_mask(other)
-        res_values = checked_add_with_arr(
-            self.asi8, -other_i8, arr_mask=self._isnan, b_mask=o_mask
-        )
+        res_values = add_overflowsafe(self.asi8, np.asarray(-other_i8, dtype="i8"))
         res_m8 = res_values.view(f"timedelta64[{self.unit}]")
 
         new_freq = self._get_arithmetic_result_freq(other)
@@ -1227,9 +1223,7 @@ def _add_timedeltalike(self, other: Timedelta | TimedeltaArray):
         self = cast("DatetimeArray | TimedeltaArray", self)
 
         other_i8, o_mask = self._get_i8_values_and_mask(other)
-        new_values = checked_add_with_arr(
-            self.asi8, other_i8, arr_mask=self._isnan, b_mask=o_mask
-        )
+        new_values = add_overflowsafe(self.asi8, np.asarray(other_i8, dtype="i8"))
         res_values = new_values.view(self._ndarray.dtype)
 
         new_freq = self._get_arithmetic_result_freq(other)
@@ -1297,9 +1291,7 @@ def _sub_periodlike(self, other: Period | PeriodArray) -> npt.NDArray[np.object_
         self._check_compatible_with(other)
 
         other_i8, o_mask = self._get_i8_values_and_mask(other)
-        new_i8_data = checked_add_with_arr(
-            self.asi8, -other_i8, arr_mask=self._isnan, b_mask=o_mask
-        )
+        new_i8_data = add_overflowsafe(self.asi8, np.asarray(-other_i8, dtype="i8"))
         new_data = np.array([self.freq.base * x for x in new_i8_data])
 
         if o_mask is None:
diff --git a/pandas/core/arrays/period.py b/pandas/core/arrays/period.py
index 1ff3896eea798..e3492dd21ea57 100644
--- a/pandas/core/arrays/period.py
+++ b/pandas/core/arrays/period.py
@@ -25,6 +25,7 @@
     NaT,
     NaTType,
     Timedelta,
+    add_overflowsafe,
     astype_overflowsafe,
     dt64arr_to_periodarr as c_dt64arr_to_periodarr,
     get_unit_from_dtype,
@@ -72,7 +73,6 @@
 )
 from pandas.core.dtypes.missing import isna
 
-import pandas.core.algorithms as algos
 from pandas.core.arrays import datetimelike as dtl
 import pandas.core.common as com
 
@@ -855,7 +855,7 @@ def _addsub_int_array_or_scalar(
         assert op in [operator.add, operator.sub]
         if op is operator.sub:
             other = -other
-        res_values = algos.checked_add_with_arr(self.asi8, other, arr_mask=self._isnan)
+        res_values = add_overflowsafe(self.asi8, np.asarray(other, dtype="i8"))
         return type(self)(res_values, dtype=self.dtype)
 
     def _add_offset(self, other: BaseOffset):
@@ -920,12 +920,7 @@ def _add_timedelta_arraylike(
                 "not an integer multiple of the PeriodArray's freq."
             ) from err
 
-        b_mask = np.isnat(delta)
-
-        res_values = algos.checked_add_with_arr(
-            self.asi8, delta.view("i8"), arr_mask=self._isnan, b_mask=b_mask
-        )
-        np.putmask(res_values, self._isnan | b_mask, iNaT)
+        res_values = add_overflowsafe(self.asi8, np.asarray(delta.view("i8")))
         return type(self)(res_values, dtype=self.dtype)
 
     def _check_timedeltalike_freq_compat(self, other):
diff --git a/pandas/tests/test_algos.py b/pandas/tests/test_algos.py
index d9162c428b492..718d1b3ee2e83 100644
--- a/pandas/tests/test_algos.py
+++ b/pandas/tests/test_algos.py
@@ -1837,57 +1837,6 @@ def test_pct_max_many_rows(self):
         assert result == 1
 
 
-def test_int64_add_overflow():
-    # see gh-14068
-    msg = "Overflow in int64 addition"
-    m = np.iinfo(np.int64).max
-    n = np.iinfo(np.int64).min
-
-    with pytest.raises(OverflowError, match=msg):
-        algos.checked_add_with_arr(np.array([m, m]), m)
-    with pytest.raises(OverflowError, match=msg):
-        algos.checked_add_with_arr(np.array([m, m]), np.array([m, m]))
-    with pytest.raises(OverflowError, match=msg):
-        algos.checked_add_with_arr(np.array([n, n]), n)
-    with pytest.raises(OverflowError, match=msg):
-        algos.checked_add_with_arr(np.array([n, n]), np.array([n, n]))
-    with pytest.raises(OverflowError, match=msg):
-        algos.checked_add_with_arr(np.array([m, n]), np.array([n, n]))
-    with pytest.raises(OverflowError, match=msg):
-        algos.checked_add_with_arr(
-            np.array([m, m]), np.array([m, m]), arr_mask=np.array([False, True])
-        )
-    with pytest.raises(OverflowError, match=msg):
-        algos.checked_add_with_arr(
-            np.array([m, m]), np.array([m, m]), b_mask=np.array([False, True])
-        )
-    with pytest.raises(OverflowError, match=msg):
-        algos.checked_add_with_arr(
-            np.array([m, m]),
-            np.array([m, m]),
-            arr_mask=np.array([False, True]),
-            b_mask=np.array([False, True]),
-        )
-    with pytest.raises(OverflowError, match=msg):
-        algos.checked_add_with_arr(np.array([m, m]), np.array([np.nan, m]))
-
-    # Check that the nan boolean arrays override whether or not
-    # the addition overflows. We don't check the result but just
-    # the fact that an OverflowError is not raised.
-    algos.checked_add_with_arr(
-        np.array([m, m]), np.array([m, m]), arr_mask=np.array([True, True])
-    )
-    algos.checked_add_with_arr(
-        np.array([m, m]), np.array([m, m]), b_mask=np.array([True, True])
-    )
-    algos.checked_add_with_arr(
-        np.array([m, m]),
-        np.array([m, m]),
-        arr_mask=np.array([True, False]),
-        b_mask=np.array([False, True]),
-    )
-
-
 class TestMode:
     def test_no_mode(self):
         exp = Series([], dtype=np.float64, index=Index([], dtype=int))
diff --git a/pandas/tests/tslibs/test_api.py b/pandas/tests/tslibs/test_api.py
index b52bc78d58296..e02cea2fef426 100644
--- a/pandas/tests/tslibs/test_api.py
+++ b/pandas/tests/tslibs/test_api.py
@@ -58,6 +58,7 @@ def test_namespace():
         "get_supported_reso",
         "npy_unit_to_abbrev",
         "guess_datetime_format",
+        "add_overflowsafe",
     ]
 
     expected = set(submodules + api)

From 8614088df2338c1db170bcd0961348220669e082 Mon Sep 17 00:00:00 2001
From: jbrockmendel <jbrockmendel@gmail.com>
Date: Sat, 9 Dec 2023 10:38:17 -0800
Subject: [PATCH 07/15] BUG: fillna with mixed-resolution dt64/td64 (#56413)

* BUG: fillna with mixed-resolution dt64/td64

* mypy fixup

* troubleshoot docbuild

* typo fixup in whatsnew
---
 doc/source/whatsnew/v2.2.0.rst             |   2 +-
 pandas/core/arrays/_mixins.py              |   6 ++
 pandas/core/arrays/datetimelike.py         |  10 +-
 pandas/tests/series/methods/test_fillna.py | 111 +++++++++++++++++----
 4 files changed, 109 insertions(+), 20 deletions(-)

diff --git a/doc/source/whatsnew/v2.2.0.rst b/doc/source/whatsnew/v2.2.0.rst
index e51a347dec46c..6006fcbcdbf20 100644
--- a/doc/source/whatsnew/v2.2.0.rst
+++ b/doc/source/whatsnew/v2.2.0.rst
@@ -537,6 +537,7 @@ Datetimelike
 - Bug in :meth:`Index.is_monotonic_increasing` and :meth:`Index.is_monotonic_decreasing` always caching :meth:`Index.is_unique` as ``True`` when first value in index is ``NaT`` (:issue:`55755`)
 - Bug in :meth:`Index.view` to a datetime64 dtype with non-supported resolution incorrectly raising (:issue:`55710`)
 - Bug in :meth:`Series.dt.round` with non-nanosecond resolution and ``NaT`` entries incorrectly raising ``OverflowError`` (:issue:`56158`)
+- Bug in :meth:`Series.fillna` with non-nanosecond resolution dtypes and higher-resolution vector values returning incorrect (internally-corrupted) results (:issue:`56410`)
 - Bug in :meth:`Tick.delta` with very large ticks raising ``OverflowError`` instead of ``OutOfBoundsTimedelta`` (:issue:`55503`)
 - Bug in :meth:`Timestamp.unit` being inferred incorrectly from an ISO8601 format string with minute or hour resolution and a timezone offset (:issue:`56208`)
 - Bug in ``.astype`` converting from a higher-resolution ``datetime64`` dtype to a lower-resolution ``datetime64`` dtype (e.g. ``datetime64[us]->datetim64[ms]``) silently overflowing with values near the lower implementation bound (:issue:`55979`)
@@ -550,7 +551,6 @@ Datetimelike
 - Bug in parsing datetime strings with nanosecond resolution with non-ISO8601 formats incorrectly truncating sub-microsecond components (:issue:`56051`)
 - Bug in parsing datetime strings with sub-second resolution and trailing zeros incorrectly inferring second or millisecond resolution (:issue:`55737`)
 - Bug in the results of :func:`to_datetime` with an floating-dtype argument with ``unit`` not matching the pointwise results of :class:`Timestamp` (:issue:`56037`)
--
 
 Timedelta
 ^^^^^^^^^
diff --git a/pandas/core/arrays/_mixins.py b/pandas/core/arrays/_mixins.py
index d6f4dbfe7f549..8d1f5262e7911 100644
--- a/pandas/core/arrays/_mixins.py
+++ b/pandas/core/arrays/_mixins.py
@@ -430,6 +430,12 @@ def _where(self: Self, mask: npt.NDArray[np.bool_], value) -> Self:
         value = self._validate_setitem_value(value)
 
         res_values = np.where(mask, self._ndarray, value)
+        if res_values.dtype != self._ndarray.dtype:
+            raise AssertionError(
+                # GH#56410
+                "Something has gone wrong, please report a bug at "
+                "github.com/pandas-dev/pandas/"
+            )
         return self._from_backing_data(res_values)
 
     # ------------------------------------------------------------------------
diff --git a/pandas/core/arrays/datetimelike.py b/pandas/core/arrays/datetimelike.py
index 879f477106ae9..8928c72de750c 100644
--- a/pandas/core/arrays/datetimelike.py
+++ b/pandas/core/arrays/datetimelike.py
@@ -646,6 +646,9 @@ def _validation_error_message(self, value, allow_listlike: bool = False) -> str:
 
     def _validate_listlike(self, value, allow_object: bool = False):
         if isinstance(value, type(self)):
+            if self.dtype.kind in "mM" and not allow_object:
+                # error: "DatetimeLikeArrayMixin" has no attribute "as_unit"
+                value = value.as_unit(self.unit, round_ok=False)  # type: ignore[attr-defined]
             return value
 
         if isinstance(value, list) and len(value) == 0:
@@ -694,6 +697,9 @@ def _validate_listlike(self, value, allow_object: bool = False):
             msg = self._validation_error_message(value, True)
             raise TypeError(msg)
 
+        if self.dtype.kind in "mM" and not allow_object:
+            # error: "DatetimeLikeArrayMixin" has no attribute "as_unit"
+            value = value.as_unit(self.unit, round_ok=False)  # type: ignore[attr-defined]
         return value
 
     def _validate_setitem_value(self, value):
@@ -2138,12 +2144,12 @@ def unit(self) -> str:
         # "ExtensionDtype"; expected "Union[DatetimeTZDtype, dtype[Any]]"
         return dtype_to_unit(self.dtype)  # type: ignore[arg-type]
 
-    def as_unit(self, unit: str) -> Self:
+    def as_unit(self, unit: str, round_ok: bool = True) -> Self:
         if unit not in ["s", "ms", "us", "ns"]:
             raise ValueError("Supported units are 's', 'ms', 'us', 'ns'")
 
         dtype = np.dtype(f"{self.dtype.kind}8[{unit}]")
-        new_values = astype_overflowsafe(self._ndarray, dtype, round_ok=True)
+        new_values = astype_overflowsafe(self._ndarray, dtype, round_ok=round_ok)
 
         if isinstance(self.dtype, np.dtype):
             new_dtype = new_values.dtype
diff --git a/pandas/tests/series/methods/test_fillna.py b/pandas/tests/series/methods/test_fillna.py
index a5170898b1720..acc5805578f22 100644
--- a/pandas/tests/series/methods/test_fillna.py
+++ b/pandas/tests/series/methods/test_fillna.py
@@ -19,6 +19,7 @@
     Timestamp,
     date_range,
     isna,
+    timedelta_range,
 )
 import pandas._testing as tm
 from pandas.core.arrays import period_array
@@ -239,7 +240,7 @@ def test_fillna_downcast_infer_objects_to_numeric(self):
         expected = Series([0, 1, 2.5, 4, 4], dtype=np.float64)
         tm.assert_series_equal(res, expected)
 
-    def test_timedelta_fillna(self, frame_or_series):
+    def test_timedelta_fillna(self, frame_or_series, unit):
         # GH#3371
         ser = Series(
             [
@@ -247,7 +248,8 @@ def test_timedelta_fillna(self, frame_or_series):
                 Timestamp("20130101"),
                 Timestamp("20130102"),
                 Timestamp("20130103 9:01:01"),
-            ]
+            ],
+            dtype=f"M8[{unit}]",
         )
         td = ser.diff()
         obj = frame_or_series(td).copy()
@@ -260,7 +262,8 @@ def test_timedelta_fillna(self, frame_or_series):
                 timedelta(0),
                 timedelta(1),
                 timedelta(days=1, seconds=9 * 3600 + 60 + 1),
-            ]
+            ],
+            dtype=f"m8[{unit}]",
         )
         expected = frame_or_series(expected)
         tm.assert_equal(result, expected)
@@ -279,7 +282,8 @@ def test_timedelta_fillna(self, frame_or_series):
                 timedelta(0),
                 timedelta(1),
                 timedelta(days=1, seconds=9 * 3600 + 60 + 1),
-            ]
+            ],
+            dtype=f"m8[{unit}]",
         )
         expected = frame_or_series(expected)
         tm.assert_equal(result, expected)
@@ -291,7 +295,8 @@ def test_timedelta_fillna(self, frame_or_series):
                 timedelta(0),
                 timedelta(1),
                 timedelta(days=1, seconds=9 * 3600 + 60 + 1),
-            ]
+            ],
+            dtype=f"m8[{unit}]",
         )
         expected = frame_or_series(expected)
         tm.assert_equal(result, expected)
@@ -303,7 +308,8 @@ def test_timedelta_fillna(self, frame_or_series):
                 timedelta(0),
                 timedelta(1),
                 timedelta(days=1, seconds=9 * 3600 + 60 + 1),
-            ]
+            ],
+            dtype=f"m8[{unit}]",
         )
         expected = frame_or_series(expected)
         tm.assert_equal(result, expected)
@@ -316,7 +322,7 @@ def test_timedelta_fillna(self, frame_or_series):
                 timedelta(1),
                 timedelta(days=1, seconds=9 * 3600 + 60 + 1),
             ],
-            dtype="m8[ns]",
+            dtype=f"m8[{unit}]",
         )
         expected = frame_or_series(expected)
         tm.assert_equal(result, expected)
@@ -375,6 +381,72 @@ def test_datetime64_fillna(self):
         )
         tm.assert_series_equal(result, expected)
 
+    @pytest.mark.parametrize(
+        "scalar",
+        [
+            False,
+            pytest.param(
+                True,
+                marks=pytest.mark.xfail(
+                    reason="GH#56410 scalar case not yet addressed"
+                ),
+            ),
+        ],
+    )
+    @pytest.mark.parametrize("tz", [None, "UTC"])
+    def test_datetime64_fillna_mismatched_reso_no_rounding(self, tz, scalar):
+        # GH#56410
+        dti = date_range("2016-01-01", periods=3, unit="s", tz=tz)
+        item = Timestamp("2016-02-03 04:05:06.789", tz=tz)
+        vec = date_range(item, periods=3, unit="ms")
+
+        exp_dtype = "M8[ms]" if tz is None else "M8[ms, UTC]"
+        expected = Series([item, dti[1], dti[2]], dtype=exp_dtype)
+
+        ser = Series(dti)
+        ser[0] = NaT
+        ser2 = ser.copy()
+
+        res = ser.fillna(item)
+        res2 = ser2.fillna(Series(vec))
+
+        if scalar:
+            tm.assert_series_equal(res, expected)
+        else:
+            tm.assert_series_equal(res2, expected)
+
+    @pytest.mark.parametrize(
+        "scalar",
+        [
+            False,
+            pytest.param(
+                True,
+                marks=pytest.mark.xfail(
+                    reason="GH#56410 scalar case not yet addressed"
+                ),
+            ),
+        ],
+    )
+    def test_timedelta64_fillna_mismatched_reso_no_rounding(self, scalar):
+        # GH#56410
+        tdi = date_range("2016-01-01", periods=3, unit="s") - Timestamp("1970-01-01")
+        item = Timestamp("2016-02-03 04:05:06.789") - Timestamp("1970-01-01")
+        vec = timedelta_range(item, periods=3, unit="ms")
+
+        expected = Series([item, tdi[1], tdi[2]], dtype="m8[ms]")
+
+        ser = Series(tdi)
+        ser[0] = NaT
+        ser2 = ser.copy()
+
+        res = ser.fillna(item)
+        res2 = ser2.fillna(Series(vec))
+
+        if scalar:
+            tm.assert_series_equal(res, expected)
+        else:
+            tm.assert_series_equal(res2, expected)
+
     def test_datetime64_fillna_backfill(self):
         # GH#6587
         # make sure that we are treating as integer when filling
@@ -392,7 +464,7 @@ def test_datetime64_fillna_backfill(self):
         tm.assert_series_equal(result, expected)
 
     @pytest.mark.parametrize("tz", ["US/Eastern", "Asia/Tokyo"])
-    def test_datetime64_tz_fillna(self, tz):
+    def test_datetime64_tz_fillna(self, tz, unit):
         # DatetimeLikeBlock
         ser = Series(
             [
@@ -400,7 +472,8 @@ def test_datetime64_tz_fillna(self, tz):
                 NaT,
                 Timestamp("2011-01-03 10:00"),
                 NaT,
-            ]
+            ],
+            dtype=f"M8[{unit}]",
         )
         null_loc = Series([False, True, False, True])
 
@@ -411,7 +484,8 @@ def test_datetime64_tz_fillna(self, tz):
                 Timestamp("2011-01-02 10:00"),
                 Timestamp("2011-01-03 10:00"),
                 Timestamp("2011-01-02 10:00"),
-            ]
+            ],
+            dtype=f"M8[{unit}]",
         )
         tm.assert_series_equal(expected, result)
         # check s is not changed
@@ -468,15 +542,18 @@ def test_datetime64_tz_fillna(self, tz):
                 Timestamp("2011-01-02 10:00"),
                 Timestamp("2011-01-03 10:00"),
                 Timestamp("2011-01-04 10:00"),
-            ]
+            ],
+            dtype=f"M8[{unit}]",
         )
         tm.assert_series_equal(expected, result)
         tm.assert_series_equal(isna(ser), null_loc)
 
         # DatetimeTZBlock
-        idx = DatetimeIndex(["2011-01-01 10:00", NaT, "2011-01-03 10:00", NaT], tz=tz)
+        idx = DatetimeIndex(
+            ["2011-01-01 10:00", NaT, "2011-01-03 10:00", NaT], tz=tz
+        ).as_unit(unit)
         ser = Series(idx)
-        assert ser.dtype == f"datetime64[ns, {tz}]"
+        assert ser.dtype == f"datetime64[{unit}, {tz}]"
         tm.assert_series_equal(isna(ser), null_loc)
 
         result = ser.fillna(Timestamp("2011-01-02 10:00"))
@@ -500,7 +577,7 @@ def test_datetime64_tz_fillna(self, tz):
                 "2011-01-02 10:00",
             ],
             tz=tz,
-        )
+        ).as_unit(unit)
         expected = Series(idx)
         tm.assert_series_equal(expected, result)
         tm.assert_series_equal(isna(ser), null_loc)
@@ -514,7 +591,7 @@ def test_datetime64_tz_fillna(self, tz):
                 "2011-01-02 10:00",
             ],
             tz=tz,
-        )
+        ).as_unit(unit)
         expected = Series(idx)
         tm.assert_series_equal(expected, result)
         tm.assert_series_equal(isna(ser), null_loc)
@@ -562,7 +639,7 @@ def test_datetime64_tz_fillna(self, tz):
                 Timestamp("2011-01-03 10:00", tz=tz),
                 Timestamp("2011-01-04 10:00", tz=tz),
             ]
-        )
+        ).dt.as_unit(unit)
         tm.assert_series_equal(expected, result)
         tm.assert_series_equal(isna(ser), null_loc)
 
@@ -589,7 +666,7 @@ def test_datetime64_tz_fillna(self, tz):
                 Timestamp("2011-01-03 10:00", tz=tz),
                 Timestamp("2013-01-01", tz="US/Pacific").tz_convert(tz),
             ]
-        )
+        ).dt.as_unit(unit)
         tm.assert_series_equal(expected, result)
         tm.assert_series_equal(isna(ser), null_loc)
 

From cb56347d1078e1c683f29e7e99ca593901d63a42 Mon Sep 17 00:00:00 2001
From: jbrockmendel <jbrockmendel@gmail.com>
Date: Sat, 9 Dec 2023 10:57:27 -0800
Subject: [PATCH 08/15] DEPR: type argument in Index.view (#56421)

---
 doc/source/whatsnew/v2.2.0.rst                |  1 +
 pandas/core/indexes/base.py                   | 10 ++++++++++
 pandas/tests/indexes/datetimes/test_setops.py |  2 +-
 pandas/tests/indexes/numeric/test_numeric.py  |  4 +++-
 pandas/tests/indexes/ranges/test_range.py     |  8 ++++++--
 pandas/tests/indexes/test_datetimelike.py     |  4 +++-
 pandas/tests/indexes/test_old_base.py         |  4 +++-
 7 files changed, 27 insertions(+), 6 deletions(-)

diff --git a/doc/source/whatsnew/v2.2.0.rst b/doc/source/whatsnew/v2.2.0.rst
index 6006fcbcdbf20..486440af46b79 100644
--- a/doc/source/whatsnew/v2.2.0.rst
+++ b/doc/source/whatsnew/v2.2.0.rst
@@ -438,6 +438,7 @@ Other Deprecations
 - Deprecated :meth:`Series.view`, use :meth:`Series.astype` instead to change the dtype (:issue:`20251`)
 - Deprecated ``core.internals`` members ``Block``, ``ExtensionBlock``, and ``DatetimeTZBlock``, use public APIs instead (:issue:`55139`)
 - Deprecated ``year``, ``month``, ``quarter``, ``day``, ``hour``, ``minute``, and ``second`` keywords in the :class:`PeriodIndex` constructor, use :meth:`PeriodIndex.from_fields` instead (:issue:`55960`)
+- Deprecated accepting a type as an argument in :meth:`Index.view`, call without any arguments instead (:issue:`55709`)
 - Deprecated allowing non-integer ``periods`` argument in :func:`date_range`, :func:`timedelta_range`, :func:`period_range`, and :func:`interval_range` (:issue:`56036`)
 - Deprecated allowing non-keyword arguments in :meth:`DataFrame.to_clipboard`. (:issue:`54229`)
 - Deprecated allowing non-keyword arguments in :meth:`DataFrame.to_csv` except ``path_or_buf``. (:issue:`54229`)
diff --git a/pandas/core/indexes/base.py b/pandas/core/indexes/base.py
index febceeb7623b5..f9f42b9788a25 100644
--- a/pandas/core/indexes/base.py
+++ b/pandas/core/indexes/base.py
@@ -1015,6 +1015,16 @@ def view(self, cls=None):
 
             result = self._data.view(cls)
         else:
+            if cls is not None:
+                warnings.warn(
+                    # GH#55709
+                    f"Passing a type in {type(self).__name__}.view is deprecated "
+                    "and will raise in a future version. "
+                    "Call view without any argument to retain the old behavior.",
+                    FutureWarning,
+                    stacklevel=find_stack_level(),
+                )
+
             result = self._view()
         if isinstance(result, Index):
             result._id = self._id
diff --git a/pandas/tests/indexes/datetimes/test_setops.py b/pandas/tests/indexes/datetimes/test_setops.py
index 3ed7fcc027a06..fc3a1d4721841 100644
--- a/pandas/tests/indexes/datetimes/test_setops.py
+++ b/pandas/tests/indexes/datetimes/test_setops.py
@@ -535,7 +535,7 @@ def test_intersection(self):
         assert isinstance(the_int, DatetimeIndex)
         assert the_int.freq == rng.freq
 
-        the_int = rng1.intersection(rng2.view(DatetimeIndex))
+        the_int = rng1.intersection(rng2)
         tm.assert_index_equal(the_int, expected)
 
         # non-overlapping
diff --git a/pandas/tests/indexes/numeric/test_numeric.py b/pandas/tests/indexes/numeric/test_numeric.py
index 944e215ee17bd..7ce55db6c0bbc 100644
--- a/pandas/tests/indexes/numeric/test_numeric.py
+++ b/pandas/tests/indexes/numeric/test_numeric.py
@@ -318,7 +318,9 @@ def test_cant_or_shouldnt_cast(self, dtype):
 
     def test_view_index(self, simple_index):
         index = simple_index
-        index.view(Index)
+        msg = "Passing a type in .*Index.view is deprecated"
+        with tm.assert_produces_warning(FutureWarning, match=msg):
+            index.view(Index)
 
     def test_prevent_casting(self, simple_index):
         index = simple_index
diff --git a/pandas/tests/indexes/ranges/test_range.py b/pandas/tests/indexes/ranges/test_range.py
index ffb2dac840198..06e19eeca6766 100644
--- a/pandas/tests/indexes/ranges/test_range.py
+++ b/pandas/tests/indexes/ranges/test_range.py
@@ -199,7 +199,9 @@ def test_view(self):
         i_view = i.view("i8")
         tm.assert_numpy_array_equal(i.values, i_view)
 
-        i_view = i.view(RangeIndex)
+        msg = "Passing a type in RangeIndex.view is deprecated"
+        with tm.assert_produces_warning(FutureWarning, match=msg):
+            i_view = i.view(RangeIndex)
         tm.assert_index_equal(i, i_view)
 
     def test_dtype(self, simple_index):
@@ -382,7 +384,9 @@ def test_cant_or_shouldnt_cast(self, start, stop, step):
 
     def test_view_index(self, simple_index):
         index = simple_index
-        index.view(Index)
+        msg = "Passing a type in RangeIndex.view is deprecated"
+        with tm.assert_produces_warning(FutureWarning, match=msg):
+            index.view(Index)
 
     def test_prevent_casting(self, simple_index):
         index = simple_index
diff --git a/pandas/tests/indexes/test_datetimelike.py b/pandas/tests/indexes/test_datetimelike.py
index 27e01427006ec..21a686e8bc05b 100644
--- a/pandas/tests/indexes/test_datetimelike.py
+++ b/pandas/tests/indexes/test_datetimelike.py
@@ -89,7 +89,9 @@ def test_view(self, simple_index):
         result = type(simple_index)(idx)
         tm.assert_index_equal(result, idx)
 
-        idx_view = idx.view(type(simple_index))
+        msg = "Passing a type in .*Index.view is deprecated"
+        with tm.assert_produces_warning(FutureWarning, match=msg):
+            idx_view = idx.view(type(simple_index))
         result = type(simple_index)(idx)
         tm.assert_index_equal(result, idx_view)
 
diff --git a/pandas/tests/indexes/test_old_base.py b/pandas/tests/indexes/test_old_base.py
index 0fff6abcfc6a5..b467e93b75e96 100644
--- a/pandas/tests/indexes/test_old_base.py
+++ b/pandas/tests/indexes/test_old_base.py
@@ -960,7 +960,9 @@ def test_view(self, simple_index):
         idx_view = idx.view(dtype)
         tm.assert_index_equal(idx, index_cls(idx_view, name="Foo"), exact=True)
 
-        idx_view = idx.view(index_cls)
+        msg = "Passing a type in .*Index.view is deprecated"
+        with tm.assert_produces_warning(FutureWarning, match=msg):
+            idx_view = idx.view(index_cls)
         tm.assert_index_equal(idx, index_cls(idx_view, name="Foo"), exact=True)
 
     def test_format(self, simple_index):

From 23c20deb7a6e7857b57abba72c15a21d8dbdfe7c Mon Sep 17 00:00:00 2001
From: Luke Manley <lukemanley@gmail.com>
Date: Sat, 9 Dec 2023 14:00:17 -0500
Subject: [PATCH 09/15] BUG: outer join on equal indexes not sorting (#56426)

* outer join on equal indexes to sort by default

* whatsnew

* fix test

* remove Index._join_precedence
---
 doc/source/whatsnew/v2.2.0.rst           |  2 +-
 pandas/core/computation/align.py         |  2 +-
 pandas/core/indexes/base.py              | 31 +++++++++---------------
 pandas/core/indexes/datetimelike.py      |  2 --
 pandas/core/reshape/merge.py             |  5 +---
 pandas/tests/indexes/multi/test_join.py  | 13 ++++------
 pandas/tests/indexes/test_base.py        | 11 +++++----
 pandas/tests/indexes/test_old_base.py    |  6 ++++-
 pandas/tests/reshape/merge/test_merge.py | 20 +++++++--------
 pandas/tests/series/test_arithmetic.py   |  3 +++
 10 files changed, 43 insertions(+), 52 deletions(-)

diff --git a/doc/source/whatsnew/v2.2.0.rst b/doc/source/whatsnew/v2.2.0.rst
index 486440af46b79..49c28e3dc5d85 100644
--- a/doc/source/whatsnew/v2.2.0.rst
+++ b/doc/source/whatsnew/v2.2.0.rst
@@ -246,7 +246,7 @@ These are bug fixes that might have notable behavior changes.
 
 In previous versions of pandas, :func:`merge` and :meth:`DataFrame.join` did not
 always return a result that followed the documented sort behavior. pandas now
-follows the documented sort behavior in merge and join operations (:issue:`54611`).
+follows the documented sort behavior in merge and join operations (:issue:`54611`, :issue:`56426`).
 
 As documented, ``sort=True`` sorts the join keys lexicographically in the resulting
 :class:`DataFrame`. With ``sort=False``, the order of the join keys depends on the
diff --git a/pandas/core/computation/align.py b/pandas/core/computation/align.py
index 85d412d044ba8..cd852ba9249cf 100644
--- a/pandas/core/computation/align.py
+++ b/pandas/core/computation/align.py
@@ -110,7 +110,7 @@ def _align_core(terms):
                 ax, itm = axis, items
 
             if not axes[ax].is_(itm):
-                axes[ax] = axes[ax].join(itm, how="outer")
+                axes[ax] = axes[ax].union(itm)
 
     for i, ndim in ndims.items():
         for axis, items in zip(range(ndim), axes):
diff --git a/pandas/core/indexes/base.py b/pandas/core/indexes/base.py
index f9f42b9788a25..9d998b46dbeed 100644
--- a/pandas/core/indexes/base.py
+++ b/pandas/core/indexes/base.py
@@ -368,9 +368,6 @@ class Index(IndexOpsMixin, PandasObject):
     Index([1, 2, 3], dtype='uint8')
     """
 
-    # To hand over control to subclasses
-    _join_precedence = 1
-
     # similar to __array_priority__, positions Index after Series and DataFrame
     #  but before ExtensionArray.  Should NOT be overridden by subclasses.
     __pandas_priority__ = 2000
@@ -4564,6 +4561,7 @@ def join(
         Index([1, 2, 3, 4, 5, 6], dtype='int64')
         """
         other = ensure_index(other)
+        sort = sort or how == "outer"
 
         if isinstance(self, ABCDatetimeIndex) and isinstance(other, ABCDatetimeIndex):
             if (self.tz is None) ^ (other.tz is None):
@@ -4614,15 +4612,6 @@ def join(
                 rindexer = np.array([])
                 return join_index, None, rindexer
 
-        if self._join_precedence < other._join_precedence:
-            flip: dict[JoinHow, JoinHow] = {"right": "left", "left": "right"}
-            how = flip.get(how, how)
-            join_index, lidx, ridx = other.join(
-                self, how=how, level=level, return_indexers=True
-            )
-            lidx, ridx = ridx, lidx
-            return join_index, lidx, ridx
-
         if self.dtype != other.dtype:
             dtype = self._find_common_type_compat(other)
             this = self.astype(dtype, copy=False)
@@ -4666,18 +4655,20 @@ def _join_via_get_indexer(
         # Note: at this point we have checked matching dtypes
 
         if how == "left":
-            join_index = self
+            join_index = self.sort_values() if sort else self
         elif how == "right":
-            join_index = other
+            join_index = other.sort_values() if sort else other
         elif how == "inner":
             join_index = self.intersection(other, sort=sort)
         elif how == "outer":
-            # TODO: sort=True here for backwards compat. It may
-            # be better to use the sort parameter passed into join
-            join_index = self.union(other)
-
-        if sort and how in ["left", "right"]:
-            join_index = join_index.sort_values()
+            try:
+                join_index = self.union(other, sort=sort)
+            except TypeError:
+                join_index = self.union(other)
+                try:
+                    join_index = _maybe_try_sort(join_index, sort)
+                except TypeError:
+                    pass
 
         if join_index is self:
             lindexer = None
diff --git a/pandas/core/indexes/datetimelike.py b/pandas/core/indexes/datetimelike.py
index 264ca8aa11495..2b03a64236128 100644
--- a/pandas/core/indexes/datetimelike.py
+++ b/pandas/core/indexes/datetimelike.py
@@ -442,8 +442,6 @@ class DatetimeTimedeltaMixin(DatetimeIndexOpsMixin, ABC):
     _is_monotonic_decreasing = Index.is_monotonic_decreasing
     _is_unique = Index.is_unique
 
-    _join_precedence = 10
-
     @property
     def unit(self) -> str:
         return self._data.unit
diff --git a/pandas/core/reshape/merge.py b/pandas/core/reshape/merge.py
index 0756b25adedcd..f07c4fb8f7d5f 100644
--- a/pandas/core/reshape/merge.py
+++ b/pandas/core/reshape/merge.py
@@ -759,7 +759,7 @@ def __init__(
         self.on = com.maybe_make_list(on)
 
         self.suffixes = suffixes
-        self.sort = sort
+        self.sort = sort or how == "outer"
 
         self.left_index = left_index
         self.right_index = right_index
@@ -1694,9 +1694,6 @@ def get_join_indexers(
         elif not sort and how in ["left", "outer"]:
             return _get_no_sort_one_missing_indexer(left_n, False)
 
-    if not sort and how == "outer":
-        sort = True
-
     # get left & right join labels and num. of levels at each location
     mapped = (
         _factorize_keys(left_keys[n], right_keys[n], sort=sort)
diff --git a/pandas/tests/indexes/multi/test_join.py b/pandas/tests/indexes/multi/test_join.py
index 700af142958b3..edd0feaaa1159 100644
--- a/pandas/tests/indexes/multi/test_join.py
+++ b/pandas/tests/indexes/multi/test_join.py
@@ -51,8 +51,11 @@ def test_join_level_corner_case(idx):
 
 
 def test_join_self(idx, join_type):
-    joined = idx.join(idx, how=join_type)
-    tm.assert_index_equal(joined, idx)
+    result = idx.join(idx, how=join_type)
+    expected = idx
+    if join_type == "outer":
+        expected = expected.sort_values()
+    tm.assert_index_equal(result, expected)
 
 
 def test_join_multi():
@@ -89,12 +92,6 @@ def test_join_multi():
     tm.assert_numpy_array_equal(ridx, exp_ridx)
 
 
-def test_join_self_unique(idx, join_type):
-    if idx.is_unique:
-        joined = idx.join(idx, how=join_type)
-        assert (idx == joined).all()
-
-
 def test_join_multi_wrong_order():
     # GH 25760
     # GH 28956
diff --git a/pandas/tests/indexes/test_base.py b/pandas/tests/indexes/test_base.py
index bb8822f047330..2b0bb884f0706 100644
--- a/pandas/tests/indexes/test_base.py
+++ b/pandas/tests/indexes/test_base.py
@@ -987,8 +987,11 @@ def test_slice_keep_name(self):
         indirect=True,
     )
     def test_join_self(self, index, join_type):
-        joined = index.join(index, how=join_type)
-        assert index is joined
+        result = index.join(index, how=join_type)
+        expected = index
+        if join_type == "outer":
+            expected = expected.sort_values()
+        tm.assert_index_equal(result, expected)
 
     @pytest.mark.parametrize("method", ["strip", "rstrip", "lstrip"])
     def test_str_attribute(self, method):
@@ -1072,10 +1075,8 @@ def test_outer_join_sort(self):
         with tm.assert_produces_warning(RuntimeWarning):
             result = left_index.join(right_index, how="outer")
 
-        # right_index in this case because DatetimeIndex has join precedence
-        # over int64 Index
         with tm.assert_produces_warning(RuntimeWarning):
-            expected = right_index.astype(object).union(left_index.astype(object))
+            expected = left_index.astype(object).union(right_index.astype(object))
 
         tm.assert_index_equal(result, expected)
 
diff --git a/pandas/tests/indexes/test_old_base.py b/pandas/tests/indexes/test_old_base.py
index b467e93b75e96..fd0d984053bd6 100644
--- a/pandas/tests/indexes/test_old_base.py
+++ b/pandas/tests/indexes/test_old_base.py
@@ -30,6 +30,7 @@
     period_range,
 )
 import pandas._testing as tm
+import pandas.core.algorithms as algos
 from pandas.core.arrays import BaseMaskedArray
 
 
@@ -653,7 +654,10 @@ def test_join_self_unique(self, join_type, simple_index):
         idx = simple_index
         if idx.is_unique:
             joined = idx.join(idx, how=join_type)
-            assert (idx == joined).all()
+            expected = simple_index
+            if join_type == "outer":
+                expected = algos.safe_sort(expected)
+            tm.assert_index_equal(joined, expected)
 
     def test_map(self, simple_index):
         # callable
diff --git a/pandas/tests/reshape/merge/test_merge.py b/pandas/tests/reshape/merge/test_merge.py
index 7538894bbf1c9..d7a343ae9f152 100644
--- a/pandas/tests/reshape/merge/test_merge.py
+++ b/pandas/tests/reshape/merge/test_merge.py
@@ -1838,6 +1838,9 @@ def test_merge_empty(self, left_empty, how, exp):
         elif exp == "empty_cross":
             expected = DataFrame(columns=["A_x", "B", "A_y", "C"], dtype="int64")
 
+        if how == "outer":
+            expected = expected.sort_values("A", ignore_index=True)
+
         tm.assert_frame_equal(result, expected)
 
 
@@ -2913,16 +2916,13 @@ def test_merge_combinations(
             expected = expected["key"].repeat(repeats.values)
             expected = expected.to_frame()
     elif how == "outer":
-        if on_index and left_unique and left["key"].equals(right["key"]):
-            expected = DataFrame({"key": left["key"]})
-        else:
-            left_counts = left["key"].value_counts()
-            right_counts = right["key"].value_counts()
-            expected_counts = left_counts.mul(right_counts, fill_value=1)
-            expected_counts = expected_counts.astype(np.intp)
-            expected = expected_counts.index.values.repeat(expected_counts.values)
-            expected = DataFrame({"key": expected})
-            expected = expected.sort_values("key")
+        left_counts = left["key"].value_counts()
+        right_counts = right["key"].value_counts()
+        expected_counts = left_counts.mul(right_counts, fill_value=1)
+        expected_counts = expected_counts.astype(np.intp)
+        expected = expected_counts.index.values.repeat(expected_counts.values)
+        expected = DataFrame({"key": expected})
+        expected = expected.sort_values("key")
 
     if on_index:
         expected = expected.set_index("key")
diff --git a/pandas/tests/series/test_arithmetic.py b/pandas/tests/series/test_arithmetic.py
index 75237be212030..b40e2e99dae2e 100644
--- a/pandas/tests/series/test_arithmetic.py
+++ b/pandas/tests/series/test_arithmetic.py
@@ -754,6 +754,9 @@ def test_series_add_tz_mismatch_converts_to_utc(self):
         uts2 = ser2.tz_convert("utc")
         expected = uts1 + uts2
 
+        # sort since input indexes are not equal
+        expected = expected.sort_index()
+
         assert result.index.tz is timezone.utc
         tm.assert_series_equal(result, expected)
 

From 71a3e3c12abd934159f43fc4d925803e063c8c6d Mon Sep 17 00:00:00 2001
From: Rob <124158982+rob-sil@users.noreply.github.com>
Date: Sat, 9 Dec 2023 13:07:44 -0600
Subject: [PATCH 10/15] BUG: `concat` should keep series names unless
 `ignore_index=True` (#56365)

* Keep series names when not ignoring them

* Split test into two shorter tests

* whatsnew

* tolist

* Split test for concat on index
---
 doc/source/whatsnew/v2.2.0.rst             |  1 +
 pandas/core/reshape/concat.py              | 22 +++++++-------
 pandas/tests/reshape/concat/test_concat.py | 35 +++++++++++++++++++---
 3 files changed, 44 insertions(+), 14 deletions(-)

diff --git a/doc/source/whatsnew/v2.2.0.rst b/doc/source/whatsnew/v2.2.0.rst
index 49c28e3dc5d85..ffefb9f41fb56 100644
--- a/doc/source/whatsnew/v2.2.0.rst
+++ b/doc/source/whatsnew/v2.2.0.rst
@@ -661,6 +661,7 @@ Groupby/resample/rolling
 Reshaping
 ^^^^^^^^^
 - Bug in :func:`concat` ignoring ``sort`` parameter when passed :class:`DatetimeIndex` indexes (:issue:`54769`)
+- Bug in :func:`concat` renaming :class:`Series` when ``ignore_index=False`` (:issue:`15047`)
 - Bug in :func:`merge_asof` raising ``TypeError`` when ``by`` dtype is not ``object``, ``int64``, or ``uint64`` (:issue:`22794`)
 - Bug in :func:`merge` returning columns in incorrect order when left and/or right is empty (:issue:`51929`)
 - Bug in :meth:`DataFrame.melt` where an exception was raised if ``var_name`` was not a string (:issue:`55948`)
diff --git a/pandas/core/reshape/concat.py b/pandas/core/reshape/concat.py
index 1bc548de91f01..d46348fff7a02 100644
--- a/pandas/core/reshape/concat.py
+++ b/pandas/core/reshape/concat.py
@@ -464,7 +464,7 @@ def __init__(
         # if we have mixed ndims, then convert to highest ndim
         # creating column numbers as needed
         if len(ndims) > 1:
-            objs, sample = self._sanitize_mixed_ndim(objs, sample, ignore_index, axis)
+            objs = self._sanitize_mixed_ndim(objs, sample, ignore_index, axis)
 
         self.objs = objs
 
@@ -580,7 +580,7 @@ def _sanitize_mixed_ndim(
         sample: Series | DataFrame,
         ignore_index: bool,
         axis: AxisInt,
-    ) -> tuple[list[Series | DataFrame], Series | DataFrame]:
+    ) -> list[Series | DataFrame]:
         # if we have mixed ndims, then convert to highest ndim
         # creating column numbers as needed
 
@@ -601,19 +601,21 @@ def _sanitize_mixed_ndim(
             else:
                 name = getattr(obj, "name", None)
                 if ignore_index or name is None:
-                    name = current_column
-                    current_column += 1
-
-                # doing a row-wise concatenation so need everything
-                # to line up
-                if self._is_frame and axis == 1:
-                    name = 0
+                    if axis == 1:
+                        # doing a row-wise concatenation so need everything
+                        # to line up
+                        name = 0
+                    else:
+                        # doing a column-wise concatenation so need series
+                        # to have unique names
+                        name = current_column
+                        current_column += 1
 
                 obj = sample._constructor({name: obj}, copy=False)
 
             new_objs.append(obj)
 
-        return new_objs, sample
+        return new_objs
 
     def get_result(self):
         cons: Callable[..., DataFrame | Series]
diff --git a/pandas/tests/reshape/concat/test_concat.py b/pandas/tests/reshape/concat/test_concat.py
index ea0d510d2b8f8..9e34d02091e69 100644
--- a/pandas/tests/reshape/concat/test_concat.py
+++ b/pandas/tests/reshape/concat/test_concat.py
@@ -267,11 +267,10 @@ def test_with_mixed_tuples(self, sort):
         # it works
         concat([df1, df2], sort=sort)
 
-    def test_concat_mixed_objs(self):
-        # concat mixed series/frames
+    def test_concat_mixed_objs_columns(self):
+        # Test column-wise concat for mixed series/frames (axis=1)
         # G2385
 
-        # axis 1
         index = date_range("01-Jan-2013", periods=10, freq="h")
         arr = np.arange(10, dtype="int64")
         s1 = Series(arr, index=index)
@@ -324,13 +323,41 @@ def test_concat_mixed_objs(self):
         result = concat([s1, df, s2], axis=1, ignore_index=True)
         tm.assert_frame_equal(result, expected)
 
-        # axis 0
+    def test_concat_mixed_objs_index(self):
+        # Test row-wise concat for mixed series/frames with a common name
+        # GH2385, GH15047
+
+        index = date_range("01-Jan-2013", periods=10, freq="h")
+        arr = np.arange(10, dtype="int64")
+        s1 = Series(arr, index=index)
+        s2 = Series(arr, index=index)
+        df = DataFrame(arr.reshape(-1, 1), index=index)
+
         expected = DataFrame(
             np.tile(arr, 3).reshape(-1, 1), index=index.tolist() * 3, columns=[0]
         )
         result = concat([s1, df, s2])
         tm.assert_frame_equal(result, expected)
 
+    def test_concat_mixed_objs_index_names(self):
+        # Test row-wise concat for mixed series/frames with distinct names
+        # GH2385, GH15047
+
+        index = date_range("01-Jan-2013", periods=10, freq="h")
+        arr = np.arange(10, dtype="int64")
+        s1 = Series(arr, index=index, name="foo")
+        s2 = Series(arr, index=index, name="bar")
+        df = DataFrame(arr.reshape(-1, 1), index=index)
+
+        expected = DataFrame(
+            np.kron(np.where(np.identity(3) == 1, 1, np.nan), arr).T,
+            index=index.tolist() * 3,
+            columns=["foo", 0, "bar"],
+        )
+        result = concat([s1, df, s2])
+        tm.assert_frame_equal(result, expected)
+
+        # Rename all series to 0 when ignore_index=True
         expected = DataFrame(np.tile(arr, 3).reshape(-1, 1), columns=[0])
         result = concat([s1, df, s2], ignore_index=True)
         tm.assert_frame_equal(result, expected)

From ce4169ac51d20786864157912072b68ae331dc52 Mon Sep 17 00:00:00 2001
From: Patrick Hoefler <61934744+phofl@users.noreply.github.com>
Date: Sat, 9 Dec 2023 20:16:53 +0100
Subject: [PATCH 11/15] Fix new string dtype tests for frame folder (#55409)

* Start fixing string tests

* BUG: interpolate raising wrong error for ea

* Fix more tests

* REGR: join segfaulting for arrow string with nulls

* Fix more tests

* Fix more tests

* BUG: rank raising for arrow string dtypes

* BUG: eq not implemented for categorical and arrow backed strings

* More tests

* BUG: ndim of string block incorrect with string inference

* Fix test

* Fix tests

* Fix tests

* Fix more indexing tests

* BUG: Index.insert raising when inserting None into new string dtype

* Fix tests

* BUG: Inserting ndim=0 array does not infer string dtype

* Fix tests

* Fix tests

* Fix more tests

* Fix more tests

* BUG: idxmax raising for arrow strings

* Fix

* Fix more tests

* Fix more tests

* Fix more tests

* Fix remaining tests

* Fix remaining tests

* Change default

* BUG: Groupby not keeping string dtype for empty objects

* Start fixing gb tests

* Fix tests

* Merge main

* Update config_init.py

* Fixup

* Update
---
 .../frame/constructors/test_from_dict.py      |   5 +
 .../frame/constructors/test_from_records.py   |   5 +
 pandas/tests/frame/indexing/test_getitem.py   |   2 +-
 pandas/tests/frame/indexing/test_indexing.py  |  35 ++++--
 pandas/tests/frame/indexing/test_set_value.py |   8 +-
 pandas/tests/frame/indexing/test_setitem.py   |   2 +-
 pandas/tests/frame/indexing/test_where.py     |   6 +-
 pandas/tests/frame/methods/test_align.py      |   4 +-
 pandas/tests/frame/methods/test_astype.py     |  22 ++--
 .../tests/frame/methods/test_combine_first.py |   6 +-
 .../frame/methods/test_convert_dtypes.py      |   6 +-
 pandas/tests/frame/methods/test_cov_corr.py   |  12 +-
 pandas/tests/frame/methods/test_drop.py       |   2 +-
 .../frame/methods/test_drop_duplicates.py     |   2 +-
 pandas/tests/frame/methods/test_dtypes.py     |   7 +-
 pandas/tests/frame/methods/test_duplicated.py |   2 +-
 pandas/tests/frame/methods/test_equals.py     |   4 +-
 pandas/tests/frame/methods/test_explode.py    |   2 +-
 pandas/tests/frame/methods/test_fillna.py     |  26 +++-
 .../frame/methods/test_get_numeric_data.py    |   6 +-
 .../tests/frame/methods/test_interpolate.py   |  13 +-
 .../methods/test_is_homogeneous_dtype.py      |   3 +-
 pandas/tests/frame/methods/test_nlargest.py   |   2 +-
 pandas/tests/frame/methods/test_rank.py       |  14 ++-
 pandas/tests/frame/methods/test_reindex.py    |   6 +-
 pandas/tests/frame/methods/test_replace.py    | 114 +++++++++++++++---
 .../tests/frame/methods/test_reset_index.py   |  12 +-
 .../tests/frame/methods/test_select_dtypes.py |  12 +-
 pandas/tests/frame/methods/test_to_csv.py     |   7 +-
 pandas/tests/frame/methods/test_update.py     |  14 ++-
 pandas/tests/frame/test_api.py                |   2 +
 pandas/tests/frame/test_arithmetic.py         |  16 ++-
 pandas/tests/frame/test_block_internals.py    |   4 +-
 pandas/tests/frame/test_constructors.py       |  39 +++---
 pandas/tests/frame/test_logical_ops.py        |  12 +-
 pandas/tests/frame/test_query_eval.py         |  19 ++-
 pandas/tests/frame/test_reductions.py         |  64 +++++++---
 pandas/tests/frame/test_repr.py               |   3 +
 pandas/tests/frame/test_stack_unstack.py      |  23 ++--
 pandas/tests/frame/test_unary.py              |  20 ++-
 pandas/tests/groupby/test_apply.py            |  29 +++--
 pandas/tests/groupby/test_categorical.py      |   5 +-
 pandas/tests/groupby/test_groupby.py          |  35 ++++--
 pandas/tests/groupby/test_numeric_only.py     |  13 +-
 pandas/tests/groupby/test_raises.py           |   2 +-
 45 files changed, 477 insertions(+), 170 deletions(-)

diff --git a/pandas/tests/frame/constructors/test_from_dict.py b/pandas/tests/frame/constructors/test_from_dict.py
index 845174bbf600e..60a8e688b3b8a 100644
--- a/pandas/tests/frame/constructors/test_from_dict.py
+++ b/pandas/tests/frame/constructors/test_from_dict.py
@@ -3,6 +3,8 @@
 import numpy as np
 import pytest
 
+from pandas._config import using_pyarrow_string_dtype
+
 from pandas import (
     DataFrame,
     Index,
@@ -42,6 +44,9 @@ def test_constructor_single_row(self):
         )
         tm.assert_frame_equal(result, expected)
 
+    @pytest.mark.skipif(
+        using_pyarrow_string_dtype(), reason="columns inferring logic broken"
+    )
     def test_constructor_list_of_series(self):
         data = [
             OrderedDict([["a", 1.5], ["b", 3.0], ["c", 4.0]]),
diff --git a/pandas/tests/frame/constructors/test_from_records.py b/pandas/tests/frame/constructors/test_from_records.py
index edb21fb92f6a2..3622571f1365d 100644
--- a/pandas/tests/frame/constructors/test_from_records.py
+++ b/pandas/tests/frame/constructors/test_from_records.py
@@ -6,6 +6,8 @@
 import pytest
 import pytz
 
+from pandas._config import using_pyarrow_string_dtype
+
 from pandas.compat import is_platform_little_endian
 
 from pandas import (
@@ -56,6 +58,9 @@ def test_from_records_with_datetimes(self):
         expected["EXPIRY"] = expected["EXPIRY"].astype("M8[s]")
         tm.assert_frame_equal(result, expected)
 
+    @pytest.mark.skipif(
+        using_pyarrow_string_dtype(), reason="dtype checking logic doesn't work"
+    )
     def test_from_records_sequencelike(self):
         df = DataFrame(
             {
diff --git a/pandas/tests/frame/indexing/test_getitem.py b/pandas/tests/frame/indexing/test_getitem.py
index 8502f98df5962..a36b0c0e850b3 100644
--- a/pandas/tests/frame/indexing/test_getitem.py
+++ b/pandas/tests/frame/indexing/test_getitem.py
@@ -103,7 +103,7 @@ def test_getitem_list_duplicates(self):
 
     def test_getitem_dupe_cols(self):
         df = DataFrame([[1, 2, 3], [4, 5, 6]], columns=["a", "a", "b"])
-        msg = "\"None of [Index(['baf'], dtype='object')] are in the [columns]\""
+        msg = "\"None of [Index(['baf'], dtype="
         with pytest.raises(KeyError, match=re.escape(msg)):
             df[["baf"]]
 
diff --git a/pandas/tests/frame/indexing/test_indexing.py b/pandas/tests/frame/indexing/test_indexing.py
index 40c6b8e180c5b..4be5be77b015c 100644
--- a/pandas/tests/frame/indexing/test_indexing.py
+++ b/pandas/tests/frame/indexing/test_indexing.py
@@ -288,7 +288,9 @@ def test_setattr_column(self):
         df.foobar = 5
         assert (df.foobar == 5).all()
 
-    def test_setitem(self, float_frame, using_copy_on_write, warn_copy_on_write):
+    def test_setitem(
+        self, float_frame, using_copy_on_write, warn_copy_on_write, using_infer_string
+    ):
         # not sure what else to do here
         series = float_frame["A"][::2]
         float_frame["col5"] = series
@@ -331,7 +333,10 @@ def test_setitem(self, float_frame, using_copy_on_write, warn_copy_on_write):
             with pytest.raises(SettingWithCopyError, match=msg):
                 smaller["col10"] = ["1", "2"]
 
-        assert smaller["col10"].dtype == np.object_
+        if using_infer_string:
+            assert smaller["col10"].dtype == "string"
+        else:
+            assert smaller["col10"].dtype == np.object_
         assert (smaller["col10"] == ["1", "2"]).all()
 
     def test_setitem2(self):
@@ -426,7 +431,7 @@ def test_setitem_cast(self, float_frame):
         float_frame["something"] = 2.5
         assert float_frame["something"].dtype == np.float64
 
-    def test_setitem_corner(self, float_frame):
+    def test_setitem_corner(self, float_frame, using_infer_string):
         # corner case
         df = DataFrame({"B": [1.0, 2.0, 3.0], "C": ["a", "b", "c"]}, index=np.arange(3))
         del df["B"]
@@ -463,10 +468,16 @@ def test_setitem_corner(self, float_frame):
         dm["foo"] = "bar"
         del dm["foo"]
         dm["foo"] = "bar"
-        assert dm["foo"].dtype == np.object_
+        if using_infer_string:
+            assert dm["foo"].dtype == "string"
+        else:
+            assert dm["foo"].dtype == np.object_
 
         dm["coercible"] = ["1", "2", "3"]
-        assert dm["coercible"].dtype == np.object_
+        if using_infer_string:
+            assert dm["coercible"].dtype == "string"
+        else:
+            assert dm["coercible"].dtype == np.object_
 
     def test_setitem_corner2(self):
         data = {
@@ -483,7 +494,7 @@ def test_setitem_corner2(self):
         assert df.loc[1, "title"] == "foobar"
         assert df.loc[1, "cruft"] == 0
 
-    def test_setitem_ambig(self):
+    def test_setitem_ambig(self, using_infer_string):
         # Difficulties with mixed-type data
         # Created as float type
         dm = DataFrame(index=range(3), columns=range(3))
@@ -499,18 +510,22 @@ def test_setitem_ambig(self):
 
         dm[2] = uncoercable_series
         assert len(dm.columns) == 3
-        assert dm[2].dtype == np.object_
+        if using_infer_string:
+            assert dm[2].dtype == "string"
+        else:
+            assert dm[2].dtype == np.object_
 
-    def test_setitem_None(self, float_frame):
+    def test_setitem_None(self, float_frame, using_infer_string):
         # GH #766
         float_frame[None] = float_frame["A"]
+        key = None if not using_infer_string else np.nan
         tm.assert_series_equal(
             float_frame.iloc[:, -1], float_frame["A"], check_names=False
         )
         tm.assert_series_equal(
-            float_frame.loc[:, None], float_frame["A"], check_names=False
+            float_frame.loc[:, key], float_frame["A"], check_names=False
         )
-        tm.assert_series_equal(float_frame[None], float_frame["A"], check_names=False)
+        tm.assert_series_equal(float_frame[key], float_frame["A"], check_names=False)
 
     def test_loc_setitem_boolean_mask_allfalse(self):
         # GH 9596
diff --git a/pandas/tests/frame/indexing/test_set_value.py b/pandas/tests/frame/indexing/test_set_value.py
index 32312868adacb..1e3c793c8449f 100644
--- a/pandas/tests/frame/indexing/test_set_value.py
+++ b/pandas/tests/frame/indexing/test_set_value.py
@@ -16,7 +16,7 @@ def test_set_value(self, float_frame):
                 float_frame._set_value(idx, col, 1)
                 assert float_frame[col][idx] == 1
 
-    def test_set_value_resize(self, float_frame):
+    def test_set_value_resize(self, float_frame, using_infer_string):
         res = float_frame._set_value("foobar", "B", 0)
         assert res is None
         assert float_frame.index[-1] == "foobar"
@@ -27,8 +27,10 @@ def test_set_value_resize(self, float_frame):
 
         res = float_frame.copy()
         res._set_value("foobar", "baz", "sam")
-        assert res["baz"].dtype == np.object_
-
+        if using_infer_string:
+            assert res["baz"].dtype == "string"
+        else:
+            assert res["baz"].dtype == np.object_
         res = float_frame.copy()
         with tm.assert_produces_warning(
             FutureWarning, match="Setting an item of incompatible dtype"
diff --git a/pandas/tests/frame/indexing/test_setitem.py b/pandas/tests/frame/indexing/test_setitem.py
index c0ba2f245efed..d0caaa3756170 100644
--- a/pandas/tests/frame/indexing/test_setitem.py
+++ b/pandas/tests/frame/indexing/test_setitem.py
@@ -1319,7 +1319,7 @@ def test_setitem_column_frame_as_category(self):
         df["col2"] = Series([1, 2, 3], dtype="category")
 
         expected_types = Series(
-            ["int64", "category", "category"], index=[0, "col1", "col2"]
+            ["int64", "category", "category"], index=[0, "col1", "col2"], dtype=object
         )
         tm.assert_series_equal(df.dtypes, expected_types)
 
diff --git a/pandas/tests/frame/indexing/test_where.py b/pandas/tests/frame/indexing/test_where.py
index 103ec67951a01..3d36d0471f02f 100644
--- a/pandas/tests/frame/indexing/test_where.py
+++ b/pandas/tests/frame/indexing/test_where.py
@@ -1077,9 +1077,13 @@ def test_where_producing_ea_cond_for_np_dtype():
 @pytest.mark.parametrize(
     "replacement", [0.001, True, "snake", None, datetime(2022, 5, 4)]
 )
-def test_where_int_overflow(replacement):
+def test_where_int_overflow(replacement, using_infer_string, request):
     # GH 31687
     df = DataFrame([[1.0, 2e25, "nine"], [np.nan, 0.1, None]])
+    if using_infer_string and replacement not in (None, "snake"):
+        request.node.add_marker(
+            pytest.mark.xfail(reason="Can't set non-string into string column")
+        )
     result = df.where(pd.notnull(df), replacement)
     expected = DataFrame([[1.0, 2e25, "nine"], [replacement, 0.1, replacement]])
 
diff --git a/pandas/tests/frame/methods/test_align.py b/pandas/tests/frame/methods/test_align.py
index 312d6f6d37dde..5a9c47866dae8 100644
--- a/pandas/tests/frame/methods/test_align.py
+++ b/pandas/tests/frame/methods/test_align.py
@@ -107,7 +107,7 @@ def test_align_float(self, float_frame, using_copy_on_write):
             af, bf = float_frame.align(
                 other.iloc[:, 0], join="inner", axis=1, method=None, fill_value=None
             )
-        tm.assert_index_equal(bf.index, Index([]))
+        tm.assert_index_equal(bf.index, Index([]).astype(bf.index.dtype))
 
         msg = (
             "The 'method', 'limit', and 'fill_axis' keywords in DataFrame.align "
@@ -117,7 +117,7 @@ def test_align_float(self, float_frame, using_copy_on_write):
             af, bf = float_frame.align(
                 other.iloc[:, 0], join="inner", axis=1, method=None, fill_value=0
             )
-        tm.assert_index_equal(bf.index, Index([]))
+        tm.assert_index_equal(bf.index, Index([]).astype(bf.index.dtype))
 
         # Try to align DataFrame to Series along bad axis
         msg = "No axis named 2 for object type DataFrame"
diff --git a/pandas/tests/frame/methods/test_astype.py b/pandas/tests/frame/methods/test_astype.py
index 2578dfb622fbf..5a1e3cd786f84 100644
--- a/pandas/tests/frame/methods/test_astype.py
+++ b/pandas/tests/frame/methods/test_astype.py
@@ -166,7 +166,8 @@ def test_astype_str(self):
                 "c": [Timedelta(x)._repr_base() for x in c._values],
                 "d": list(map(str, d._values)),
                 "e": list(map(str, e._values)),
-            }
+            },
+            dtype="object",
         )
 
         tm.assert_frame_equal(result, expected)
@@ -174,13 +175,13 @@ def test_astype_str(self):
     def test_astype_str_float(self):
         # see GH#11302
         result = DataFrame([np.nan]).astype(str)
-        expected = DataFrame(["nan"])
+        expected = DataFrame(["nan"], dtype="object")
 
         tm.assert_frame_equal(result, expected)
         result = DataFrame([1.12345678901234567890]).astype(str)
 
         val = "1.1234567890123457"
-        expected = DataFrame([val])
+        expected = DataFrame([val], dtype="object")
         tm.assert_frame_equal(result, expected)
 
     @pytest.mark.parametrize("dtype_class", [dict, Series])
@@ -199,7 +200,7 @@ def test_astype_dict_like(self, dtype_class):
         expected = DataFrame(
             {
                 "a": a,
-                "b": Series(["0", "1", "2", "3", "4"]),
+                "b": Series(["0", "1", "2", "3", "4"], dtype="object"),
                 "c": c,
                 "d": Series([1.0, 2.0, 3.14, 4.0, 5.4], dtype="float32"),
             }
@@ -282,7 +283,7 @@ def test_astype_duplicate_col_series_arg(self):
         result = df.astype(dtypes)
         expected = DataFrame(
             {
-                0: vals[:, 0].astype(str),
+                0: Series(vals[:, 0].astype(str), dtype=object),
                 1: vals[:, 1],
                 2: pd.array(vals[:, 2], dtype="Float64"),
                 3: vals[:, 3],
@@ -620,6 +621,7 @@ def test_astype_arg_for_errors_dictlist(self):
                 {"a": 2.2, "b": "15.3", "c": "another_test"},
             ]
         )
+        expected["c"] = expected["c"].astype("object")
         type_dict = {"a": "float64", "b": "float64", "c": "object"}
 
         result = df.astype(dtype=type_dict, errors="ignore")
@@ -680,6 +682,7 @@ def test_astype_dt64tz_to_str(self, timezone_frame):
                 ],
             ],
             columns=timezone_frame.columns,
+            dtype="object",
         )
         tm.assert_frame_equal(result, expected)
 
@@ -754,7 +757,9 @@ def test_astype_tz_object_conversion(self, tz):
         result = result.astype({"tz": "datetime64[ns, Europe/London]"})
         tm.assert_frame_equal(result, expected)
 
-    def test_astype_dt64_to_string(self, frame_or_series, tz_naive_fixture):
+    def test_astype_dt64_to_string(
+        self, frame_or_series, tz_naive_fixture, using_infer_string
+    ):
         # GH#41409
         tz = tz_naive_fixture
 
@@ -772,7 +777,10 @@ def test_astype_dt64_to_string(self, frame_or_series, tz_naive_fixture):
         item = result.iloc[0]
         if frame_or_series is DataFrame:
             item = item.iloc[0]
-        assert item is pd.NA
+        if using_infer_string:
+            assert item is np.nan
+        else:
+            assert item is pd.NA
 
         # For non-NA values, we should match what we get for non-EA str
         alt = obj.astype(str)
diff --git a/pandas/tests/frame/methods/test_combine_first.py b/pandas/tests/frame/methods/test_combine_first.py
index 0335279b3a123..941e4c03464ea 100644
--- a/pandas/tests/frame/methods/test_combine_first.py
+++ b/pandas/tests/frame/methods/test_combine_first.py
@@ -30,7 +30,7 @@ def test_combine_first_mixed(self):
         combined = f.combine_first(g)
         tm.assert_frame_equal(combined, exp)
 
-    def test_combine_first(self, float_frame):
+    def test_combine_first(self, float_frame, using_infer_string):
         # disjoint
         head, tail = float_frame[:5], float_frame[5:]
 
@@ -76,7 +76,9 @@ def test_combine_first(self, float_frame):
         tm.assert_series_equal(combined["A"].reindex(g.index), g["A"])
 
         # corner cases
-        comb = float_frame.combine_first(DataFrame())
+        warning = FutureWarning if using_infer_string else None
+        with tm.assert_produces_warning(warning, match="empty entries"):
+            comb = float_frame.combine_first(DataFrame())
         tm.assert_frame_equal(comb, float_frame)
 
         comb = DataFrame().combine_first(float_frame)
diff --git a/pandas/tests/frame/methods/test_convert_dtypes.py b/pandas/tests/frame/methods/test_convert_dtypes.py
index 4c371afcc4e00..a181a271181ca 100644
--- a/pandas/tests/frame/methods/test_convert_dtypes.py
+++ b/pandas/tests/frame/methods/test_convert_dtypes.py
@@ -11,9 +11,13 @@ class TestConvertDtypes:
     @pytest.mark.parametrize(
         "convert_integer, expected", [(False, np.dtype("int32")), (True, "Int32")]
     )
-    def test_convert_dtypes(self, convert_integer, expected, string_storage):
+    def test_convert_dtypes(
+        self, convert_integer, expected, string_storage, using_infer_string
+    ):
         # Specific types are tested in tests/series/test_dtypes.py
         # Just check that it works for DataFrame here
+        if using_infer_string:
+            string_storage = "pyarrow_numpy"
         df = pd.DataFrame(
             {
                 "a": pd.Series([1, 2, 3], dtype=np.dtype("int32")),
diff --git a/pandas/tests/frame/methods/test_cov_corr.py b/pandas/tests/frame/methods/test_cov_corr.py
index 108816697ef3e..04a08c8b9bc52 100644
--- a/pandas/tests/frame/methods/test_cov_corr.py
+++ b/pandas/tests/frame/methods/test_cov_corr.py
@@ -326,7 +326,7 @@ def test_corrwith(self, datetime_frame, dtype):
         for row in index[:4]:
             tm.assert_almost_equal(correls[row], df1.loc[row].corr(df2.loc[row]))
 
-    def test_corrwith_with_objects(self):
+    def test_corrwith_with_objects(self, using_infer_string):
         df1 = DataFrame(
             np.random.default_rng(2).standard_normal((10, 4)),
             columns=Index(list("ABCD"), dtype=object),
@@ -338,8 +338,14 @@ def test_corrwith_with_objects(self):
         df1["obj"] = "foo"
         df2["obj"] = "bar"
 
-        with pytest.raises(TypeError, match="Could not convert"):
-            df1.corrwith(df2)
+        if using_infer_string:
+            import pyarrow as pa
+
+            with pytest.raises(pa.lib.ArrowNotImplementedError, match="has no kernel"):
+                df1.corrwith(df2)
+        else:
+            with pytest.raises(TypeError, match="Could not convert"):
+                df1.corrwith(df2)
         result = df1.corrwith(df2, numeric_only=True)
         expected = df1.loc[:, cols].corrwith(df2.loc[:, cols])
         tm.assert_series_equal(result, expected)
diff --git a/pandas/tests/frame/methods/test_drop.py b/pandas/tests/frame/methods/test_drop.py
index f72c0594fa1f7..06cd51b43a0aa 100644
--- a/pandas/tests/frame/methods/test_drop.py
+++ b/pandas/tests/frame/methods/test_drop.py
@@ -510,7 +510,7 @@ def test_drop_with_duplicate_columns2(self):
 
     def test_drop_inplace_no_leftover_column_reference(self):
         # GH 13934
-        df = DataFrame({"a": [1, 2, 3]})
+        df = DataFrame({"a": [1, 2, 3]}, columns=Index(["a"], dtype="object"))
         a = df.a
         df.drop(["a"], axis=1, inplace=True)
         tm.assert_index_equal(df.columns, Index([], dtype="object"))
diff --git a/pandas/tests/frame/methods/test_drop_duplicates.py b/pandas/tests/frame/methods/test_drop_duplicates.py
index df12139258a6d..6bea97b2cf189 100644
--- a/pandas/tests/frame/methods/test_drop_duplicates.py
+++ b/pandas/tests/frame/methods/test_drop_duplicates.py
@@ -16,7 +16,7 @@
 def test_drop_duplicates_with_misspelled_column_name(subset):
     # GH 19730
     df = DataFrame({"A": [0, 0, 1], "B": [0, 0, 1], "C": [0, 0, 1]})
-    msg = re.escape("Index(['a'], dtype='object')")
+    msg = re.escape("Index(['a'], dtype=")
 
     with pytest.raises(KeyError, match=msg):
         df.drop_duplicates(subset)
diff --git a/pandas/tests/frame/methods/test_dtypes.py b/pandas/tests/frame/methods/test_dtypes.py
index 4bdf16977dae6..ab632ac17318e 100644
--- a/pandas/tests/frame/methods/test_dtypes.py
+++ b/pandas/tests/frame/methods/test_dtypes.py
@@ -142,9 +142,12 @@ def test_dtypes_timedeltas(self):
         )
         tm.assert_series_equal(result, expected)
 
-    def test_frame_apply_np_array_return_type(self):
+    def test_frame_apply_np_array_return_type(self, using_infer_string):
         # GH 35517
         df = DataFrame([["foo"]])
         result = df.apply(lambda col: np.array("bar"))
-        expected = Series(["bar"])
+        if using_infer_string:
+            expected = Series([np.array(["bar"])])
+        else:
+            expected = Series(["bar"])
         tm.assert_series_equal(result, expected)
diff --git a/pandas/tests/frame/methods/test_duplicated.py b/pandas/tests/frame/methods/test_duplicated.py
index 788aede805110..6052b61ea8db5 100644
--- a/pandas/tests/frame/methods/test_duplicated.py
+++ b/pandas/tests/frame/methods/test_duplicated.py
@@ -16,7 +16,7 @@
 def test_duplicated_with_misspelled_column_name(subset):
     # GH 19730
     df = DataFrame({"A": [0, 0, 1], "B": [0, 0, 1], "C": [0, 0, 1]})
-    msg = re.escape("Index(['a'], dtype='object')")
+    msg = re.escape("Index(['a'], dtype=")
 
     with pytest.raises(KeyError, match=msg):
         df.duplicated(subset)
diff --git a/pandas/tests/frame/methods/test_equals.py b/pandas/tests/frame/methods/test_equals.py
index 6fcf670f96ef0..d0b9d96cafa0d 100644
--- a/pandas/tests/frame/methods/test_equals.py
+++ b/pandas/tests/frame/methods/test_equals.py
@@ -14,11 +14,11 @@ def test_dataframe_not_equal(self):
         df2 = DataFrame({"a": ["s", "d"], "b": [1, 2]})
         assert df1.equals(df2) is False
 
-    def test_equals_different_blocks(self, using_array_manager):
+    def test_equals_different_blocks(self, using_array_manager, using_infer_string):
         # GH#9330
         df0 = DataFrame({"A": ["x", "y"], "B": [1, 2], "C": ["w", "z"]})
         df1 = df0.reset_index()[["A", "B", "C"]]
-        if not using_array_manager:
+        if not using_array_manager and not using_infer_string:
             # this assert verifies that the above operations have
             # induced a block rearrangement
             assert df0._mgr.blocks[0].dtype != df1._mgr.blocks[0].dtype
diff --git a/pandas/tests/frame/methods/test_explode.py b/pandas/tests/frame/methods/test_explode.py
index d1e4a603c5710..5cd54db62d783 100644
--- a/pandas/tests/frame/methods/test_explode.py
+++ b/pandas/tests/frame/methods/test_explode.py
@@ -203,7 +203,7 @@ def test_usecase():
 )
 def test_duplicate_index(input_dict, input_index, expected_dict, expected_index):
     # GH 28005
-    df = pd.DataFrame(input_dict, index=input_index)
+    df = pd.DataFrame(input_dict, index=input_index, dtype=object)
     result = df.explode("col1")
     expected = pd.DataFrame(expected_dict, index=expected_index, dtype=object)
     tm.assert_frame_equal(result, expected)
diff --git a/pandas/tests/frame/methods/test_fillna.py b/pandas/tests/frame/methods/test_fillna.py
index 960f05a6457a4..1403a45a5cccd 100644
--- a/pandas/tests/frame/methods/test_fillna.py
+++ b/pandas/tests/frame/methods/test_fillna.py
@@ -1,6 +1,8 @@
 import numpy as np
 import pytest
 
+from pandas._config import using_pyarrow_string_dtype
+
 import pandas.util._test_decorators as td
 
 from pandas import (
@@ -89,6 +91,7 @@ def test_fillna_datetime(self, datetime_frame):
         with pytest.raises(ValueError, match=msg):
             datetime_frame.fillna(5, method="ffill")
 
+    @pytest.mark.xfail(using_pyarrow_string_dtype(), reason="can't fill 0 in string")
     def test_fillna_mixed_type(self, float_string_frame):
         mf = float_string_frame
         mf.loc[mf.index[5:20], "foo"] = np.nan
@@ -122,19 +125,27 @@ def test_fillna_empty(self, using_copy_on_write):
                 df.x.fillna(method=m, inplace=True)
                 df.x.fillna(method=m)
 
-    def test_fillna_different_dtype(self):
+    def test_fillna_different_dtype(self, using_infer_string):
         # with different dtype (GH#3386)
         df = DataFrame(
             [["a", "a", np.nan, "a"], ["b", "b", np.nan, "b"], ["c", "c", np.nan, "c"]]
         )
 
-        result = df.fillna({2: "foo"})
+        if using_infer_string:
+            with tm.assert_produces_warning(FutureWarning, match="Downcasting"):
+                result = df.fillna({2: "foo"})
+        else:
+            result = df.fillna({2: "foo"})
         expected = DataFrame(
             [["a", "a", "foo", "a"], ["b", "b", "foo", "b"], ["c", "c", "foo", "c"]]
         )
         tm.assert_frame_equal(result, expected)
 
-        return_value = df.fillna({2: "foo"}, inplace=True)
+        if using_infer_string:
+            with tm.assert_produces_warning(FutureWarning, match="Downcasting"):
+                return_value = df.fillna({2: "foo"}, inplace=True)
+        else:
+            return_value = df.fillna({2: "foo"}, inplace=True)
         tm.assert_frame_equal(df, expected)
         assert return_value is None
 
@@ -358,7 +369,7 @@ def test_fillna_dictlike_value_duplicate_colnames(self, columns):
         expected["A"] = 0.0
         tm.assert_frame_equal(result, expected)
 
-    def test_fillna_dtype_conversion(self):
+    def test_fillna_dtype_conversion(self, using_infer_string):
         # make sure that fillna on an empty frame works
         df = DataFrame(index=["A", "B", "C"], columns=[1, 2, 3, 4, 5])
         result = df.dtypes
@@ -373,7 +384,11 @@ def test_fillna_dtype_conversion(self):
 
         # empty block
         df = DataFrame(index=range(3), columns=["A", "B"], dtype="float64")
-        result = df.fillna("nan")
+        if using_infer_string:
+            with tm.assert_produces_warning(FutureWarning, match="Downcasting"):
+                result = df.fillna("nan")
+        else:
+            result = df.fillna("nan")
         expected = DataFrame("nan", index=range(3), columns=["A", "B"])
         tm.assert_frame_equal(result, expected)
 
@@ -649,6 +664,7 @@ def test_fillna_col_reordering(self):
             filled = df.fillna(method="ffill")
         assert df.columns.tolist() == filled.columns.tolist()
 
+    @pytest.mark.xfail(using_pyarrow_string_dtype(), reason="can't fill 0 in string")
     def test_fill_corner(self, float_frame, float_string_frame):
         mf = float_string_frame
         mf.loc[mf.index[5:20], "foo"] = np.nan
diff --git a/pandas/tests/frame/methods/test_get_numeric_data.py b/pandas/tests/frame/methods/test_get_numeric_data.py
index ec1c768603a59..c5d32d56d03c1 100644
--- a/pandas/tests/frame/methods/test_get_numeric_data.py
+++ b/pandas/tests/frame/methods/test_get_numeric_data.py
@@ -15,12 +15,12 @@
 class TestGetNumericData:
     def test_get_numeric_data_preserve_dtype(self):
         # get the numeric data
-        obj = DataFrame({"A": [1, "2", 3.0]})
+        obj = DataFrame({"A": [1, "2", 3.0]}, columns=Index(["A"], dtype="object"))
         result = obj._get_numeric_data()
         expected = DataFrame(dtype=object, index=pd.RangeIndex(3), columns=[])
         tm.assert_frame_equal(result, expected)
 
-    def test_get_numeric_data(self):
+    def test_get_numeric_data(self, using_infer_string):
         datetime64name = np.dtype("M8[s]").name
         objectname = np.dtype(np.object_).name
 
@@ -33,7 +33,7 @@ def test_get_numeric_data(self):
             [
                 np.dtype("float64"),
                 np.dtype("int64"),
-                np.dtype(objectname),
+                np.dtype(objectname) if not using_infer_string else "string",
                 np.dtype(datetime64name),
             ],
             index=["a", "b", "c", "f"],
diff --git a/pandas/tests/frame/methods/test_interpolate.py b/pandas/tests/frame/methods/test_interpolate.py
index 5f37ed6d9e18a..e0641fcb65bd3 100644
--- a/pandas/tests/frame/methods/test_interpolate.py
+++ b/pandas/tests/frame/methods/test_interpolate.py
@@ -1,6 +1,8 @@
 import numpy as np
 import pytest
 
+from pandas._config import using_pyarrow_string_dtype
+
 from pandas.errors import ChainedAssignmentError
 import pandas.util._test_decorators as td
 
@@ -67,6 +69,9 @@ def test_interpolate_inplace(self, frame_or_series, using_array_manager, request
         assert np.shares_memory(orig, obj.values)
         assert orig.squeeze()[1] == 1.5
 
+    @pytest.mark.xfail(
+        using_pyarrow_string_dtype(), reason="interpolate doesn't work for string"
+    )
     def test_interp_basic(self, using_copy_on_write):
         df = DataFrame(
             {
@@ -108,7 +113,10 @@ def test_interp_basic(self, using_copy_on_write):
         assert np.shares_memory(df["C"]._values, cvalues)
         assert np.shares_memory(df["D"]._values, dvalues)
 
-    def test_interp_basic_with_non_range_index(self):
+    @pytest.mark.xfail(
+        using_pyarrow_string_dtype(), reason="interpolate doesn't work for string"
+    )
+    def test_interp_basic_with_non_range_index(self, using_infer_string):
         df = DataFrame(
             {
                 "A": [1, 2, np.nan, 4],
@@ -119,7 +127,8 @@ def test_interp_basic_with_non_range_index(self):
         )
 
         msg = "DataFrame.interpolate with object dtype"
-        with tm.assert_produces_warning(FutureWarning, match=msg):
+        warning = FutureWarning if not using_infer_string else None
+        with tm.assert_produces_warning(warning, match=msg):
             result = df.set_index("C").interpolate()
         expected = df.set_index("C")
         expected.loc[3, "A"] = 3
diff --git a/pandas/tests/frame/methods/test_is_homogeneous_dtype.py b/pandas/tests/frame/methods/test_is_homogeneous_dtype.py
index a5f285d31301b..1fe28cb8eb856 100644
--- a/pandas/tests/frame/methods/test_is_homogeneous_dtype.py
+++ b/pandas/tests/frame/methods/test_is_homogeneous_dtype.py
@@ -25,7 +25,8 @@
                 {
                     "A": np.array([1, 2], dtype=object),
                     "B": np.array(["a", "b"], dtype=object),
-                }
+                },
+                dtype="object",
             ),
             True,
         ),
diff --git a/pandas/tests/frame/methods/test_nlargest.py b/pandas/tests/frame/methods/test_nlargest.py
index 1196f8cd3886a..3ba893501914a 100644
--- a/pandas/tests/frame/methods/test_nlargest.py
+++ b/pandas/tests/frame/methods/test_nlargest.py
@@ -86,7 +86,7 @@ def test_nlargest_n(self, df_strings, nselect_method, n, order):
         df = df_strings
         if "b" in order:
             error_msg = (
-                f"Column 'b' has dtype object, "
+                f"Column 'b' has dtype (object|string), "
                 f"cannot use method '{nselect_method}' with this dtype"
             )
             with pytest.raises(TypeError, match=error_msg):
diff --git a/pandas/tests/frame/methods/test_rank.py b/pandas/tests/frame/methods/test_rank.py
index b5b5e42691e59..8d7a0b373f5f8 100644
--- a/pandas/tests/frame/methods/test_rank.py
+++ b/pandas/tests/frame/methods/test_rank.py
@@ -13,6 +13,7 @@
 
 from pandas import (
     DataFrame,
+    Index,
     Series,
 )
 import pandas._testing as tm
@@ -469,21 +470,28 @@ def test_rank_inf_nans_na_option(
             ("top", False, [2.0, 3.0, 1.0, 4.0]),
         ],
     )
-    def test_rank_object_first(self, frame_or_series, na_option, ascending, expected):
+    def test_rank_object_first(
+        self, frame_or_series, na_option, ascending, expected, using_infer_string
+    ):
         obj = frame_or_series(["foo", "foo", None, "foo"])
         result = obj.rank(method="first", na_option=na_option, ascending=ascending)
         expected = frame_or_series(expected)
+        if using_infer_string and isinstance(obj, Series):
+            expected = expected.astype("uint64")
         tm.assert_equal(result, expected)
 
     @pytest.mark.parametrize(
         "data,expected",
         [
-            ({"a": [1, 2, "a"], "b": [4, 5, 6]}, DataFrame({"b": [1.0, 2.0, 3.0]})),
+            (
+                {"a": [1, 2, "a"], "b": [4, 5, 6]},
+                DataFrame({"b": [1.0, 2.0, 3.0]}, columns=Index(["b"], dtype=object)),
+            ),
             ({"a": [1, 2, "a"]}, DataFrame(index=range(3), columns=[])),
         ],
     )
     def test_rank_mixed_axis_zero(self, data, expected):
-        df = DataFrame(data)
+        df = DataFrame(data, columns=Index(list(data.keys()), dtype=object))
         with pytest.raises(TypeError, match="'<' not supported between instances of"):
             df.rank()
         result = df.rank(numeric_only=True)
diff --git a/pandas/tests/frame/methods/test_reindex.py b/pandas/tests/frame/methods/test_reindex.py
index d0d971e29204a..d862e14ce86cb 100644
--- a/pandas/tests/frame/methods/test_reindex.py
+++ b/pandas/tests/frame/methods/test_reindex.py
@@ -120,7 +120,7 @@ def test_reindex_timestamp_with_fold(self, timezone, year, month, day, hour):
         exp = DataFrame({"index": ["1", "2"], "vals": [np.nan, np.nan]}).set_index(
             "index"
         )
-        exp = exp.astype(object)
+        exp = exp.astype(df.vals.dtype)
         tm.assert_frame_equal(
             df,
             exp,
@@ -840,8 +840,8 @@ def test_reindex_fill_value(self):
 
         # other dtypes
         df["foo"] = "foo"
-        result = df.reindex(range(15), fill_value=0)
-        expected = df.reindex(range(15)).fillna(0)
+        result = df.reindex(range(15), fill_value="0")
+        expected = df.reindex(range(15)).fillna("0")
         tm.assert_frame_equal(result, expected)
 
     def test_reindex_uint_dtypes_fill_value(self, any_unsigned_int_numpy_dtype):
diff --git a/pandas/tests/frame/methods/test_replace.py b/pandas/tests/frame/methods/test_replace.py
index 53c45a5f4b5c6..8bfa98042eb07 100644
--- a/pandas/tests/frame/methods/test_replace.py
+++ b/pandas/tests/frame/methods/test_replace.py
@@ -6,6 +6,8 @@
 import numpy as np
 import pytest
 
+from pandas._config import using_pyarrow_string_dtype
+
 import pandas as pd
 from pandas import (
     DataFrame,
@@ -28,6 +30,9 @@ def mix_abc() -> dict[str, list[float | str]]:
 
 
 class TestDataFrameReplace:
+    @pytest.mark.xfail(
+        using_pyarrow_string_dtype(), reason="can't set float into string"
+    )
     def test_replace_inplace(self, datetime_frame, float_string_frame):
         datetime_frame.loc[datetime_frame.index[:5], "A"] = np.nan
         datetime_frame.loc[datetime_frame.index[-5:], "A"] = np.nan
@@ -278,14 +283,25 @@ def test_regex_replace_dict_nested(self, mix_abc):
         tm.assert_frame_equal(res3, expec)
         tm.assert_frame_equal(res4, expec)
 
-    def test_regex_replace_dict_nested_non_first_character(self, any_string_dtype):
+    def test_regex_replace_dict_nested_non_first_character(
+        self, any_string_dtype, using_infer_string
+    ):
         # GH 25259
         dtype = any_string_dtype
         df = DataFrame({"first": ["abc", "bca", "cab"]}, dtype=dtype)
-        expected = DataFrame({"first": [".bc", "bc.", "c.b"]}, dtype=dtype)
-        result = df.replace({"a": "."}, regex=True)
+        if using_infer_string and any_string_dtype == "object":
+            with tm.assert_produces_warning(FutureWarning, match="Downcasting"):
+                result = df.replace({"a": "."}, regex=True)
+            expected = DataFrame({"first": [".bc", "bc.", "c.b"]})
+
+        else:
+            result = df.replace({"a": "."}, regex=True)
+            expected = DataFrame({"first": [".bc", "bc.", "c.b"]}, dtype=dtype)
         tm.assert_frame_equal(result, expected)
 
+    @pytest.mark.xfail(
+        using_pyarrow_string_dtype(), reason="can't set float into string"
+    )
     def test_regex_replace_dict_nested_gh4115(self):
         df = DataFrame({"Type": ["Q", "T", "Q", "Q", "T"], "tmp": 2})
         expected = DataFrame({"Type": [0, 1, 0, 0, 1], "tmp": 2})
@@ -294,6 +310,9 @@ def test_regex_replace_dict_nested_gh4115(self):
             result = df.replace({"Type": {"Q": 0, "T": 1}})
         tm.assert_frame_equal(result, expected)
 
+    @pytest.mark.xfail(
+        using_pyarrow_string_dtype(), reason="can't set float into string"
+    )
     def test_regex_replace_list_to_scalar(self, mix_abc):
         df = DataFrame(mix_abc)
         expec = DataFrame(
@@ -322,6 +341,9 @@ def test_regex_replace_list_to_scalar(self, mix_abc):
         tm.assert_frame_equal(res2, expec)
         tm.assert_frame_equal(res3, expec)
 
+    @pytest.mark.xfail(
+        using_pyarrow_string_dtype(), reason="can't set float into string"
+    )
     def test_regex_replace_str_to_numeric(self, mix_abc):
         # what happens when you try to replace a numeric value with a regex?
         df = DataFrame(mix_abc)
@@ -337,6 +359,9 @@ def test_regex_replace_str_to_numeric(self, mix_abc):
         tm.assert_frame_equal(res2, expec)
         tm.assert_frame_equal(res3, expec)
 
+    @pytest.mark.xfail(
+        using_pyarrow_string_dtype(), reason="can't set float into string"
+    )
     def test_regex_replace_regex_list_to_numeric(self, mix_abc):
         df = DataFrame(mix_abc)
         res = df.replace([r"\s*\.\s*", "b"], 0, regex=True)
@@ -415,12 +440,31 @@ def test_replace_regex_metachar(self, metachar):
         ],
     )
     def test_regex_replace_string_types(
-        self, data, to_replace, expected, frame_or_series, any_string_dtype
+        self,
+        data,
+        to_replace,
+        expected,
+        frame_or_series,
+        any_string_dtype,
+        using_infer_string,
+        request,
     ):
         # GH-41333, GH-35977
         dtype = any_string_dtype
         obj = frame_or_series(data, dtype=dtype)
-        result = obj.replace(to_replace, regex=True)
+        if using_infer_string and any_string_dtype == "object":
+            if len(to_replace) > 1 and isinstance(obj, DataFrame):
+                request.node.add_marker(
+                    pytest.mark.xfail(
+                        reason="object input array that gets downcasted raises on "
+                        "second pass"
+                    )
+                )
+            with tm.assert_produces_warning(FutureWarning, match="Downcasting"):
+                result = obj.replace(to_replace, regex=True)
+                dtype = "string[pyarrow_numpy]"
+        else:
+            result = obj.replace(to_replace, regex=True)
         expected = frame_or_series(expected, dtype=dtype)
 
         tm.assert_equal(result, expected)
@@ -522,6 +566,9 @@ def test_replace_series_dict(self):
         result = df.replace(s, df.mean())
         tm.assert_frame_equal(result, expected)
 
+    @pytest.mark.xfail(
+        using_pyarrow_string_dtype(), reason="can't set float into string"
+    )
     def test_replace_convert(self):
         # gh 3907
         df = DataFrame([["foo", "bar", "bah"], ["bar", "foo", "bah"]])
@@ -533,6 +580,9 @@ def test_replace_convert(self):
         res = rep.dtypes
         tm.assert_series_equal(expec, res)
 
+    @pytest.mark.xfail(
+        using_pyarrow_string_dtype(), reason="can't set float into string"
+    )
     def test_replace_mixed(self, float_string_frame):
         mf = float_string_frame
         mf.iloc[5:20, mf.columns.get_loc("foo")] = np.nan
@@ -588,7 +638,7 @@ def test_replace_mixed_int_block_splitting(self):
         result = df.replace(0, 0.5)
         tm.assert_frame_equal(result, expected)
 
-    def test_replace_mixed2(self):
+    def test_replace_mixed2(self, using_infer_string):
         # to object block upcasting
         df = DataFrame(
             {
@@ -607,11 +657,15 @@ def test_replace_mixed2(self):
 
         expected = DataFrame(
             {
-                "A": Series(["foo", "bar"], dtype="object"),
+                "A": Series(["foo", "bar"]),
                 "B": Series([0, "foo"], dtype="object"),
             }
         )
-        result = df.replace([1, 2], ["foo", "bar"])
+        if using_infer_string:
+            with tm.assert_produces_warning(FutureWarning, match="Downcasting"):
+                result = df.replace([1, 2], ["foo", "bar"])
+        else:
+            result = df.replace([1, 2], ["foo", "bar"])
         tm.assert_frame_equal(result, expected)
 
     def test_replace_mixed3(self):
@@ -892,6 +946,9 @@ def test_replace_input_formats_listlike(self):
         with pytest.raises(ValueError, match=msg):
             df.replace(to_rep, values[1:])
 
+    @pytest.mark.xfail(
+        using_pyarrow_string_dtype(), reason="can't set float into string"
+    )
     def test_replace_input_formats_scalar(self):
         df = DataFrame(
             {"A": [np.nan, 0, np.inf], "B": [0, 2, 5], "C": ["", "asdf", "fd"]}
@@ -920,6 +977,9 @@ def test_replace_limit(self):
         # TODO
         pass
 
+    @pytest.mark.xfail(
+        using_pyarrow_string_dtype(), reason="can't set float into string"
+    )
     def test_replace_dict_no_regex(self):
         answer = Series(
             {
@@ -943,6 +1003,9 @@ def test_replace_dict_no_regex(self):
             result = answer.replace(weights)
         tm.assert_series_equal(result, expected)
 
+    @pytest.mark.xfail(
+        using_pyarrow_string_dtype(), reason="can't set float into string"
+    )
     def test_replace_series_no_regex(self):
         answer = Series(
             {
@@ -1049,7 +1112,10 @@ def test_nested_dict_overlapping_keys_replace_str(self):
         expected = df.replace({"a": dict(zip(astr, bstr))})
         tm.assert_frame_equal(result, expected)
 
-    def test_replace_swapping_bug(self):
+    @pytest.mark.xfail(
+        using_pyarrow_string_dtype(), reason="can't set float into string"
+    )
+    def test_replace_swapping_bug(self, using_infer_string):
         df = DataFrame({"a": [True, False, True]})
         res = df.replace({"a": {True: "Y", False: "N"}})
         expect = DataFrame({"a": ["Y", "N", "Y"]})
@@ -1060,6 +1126,9 @@ def test_replace_swapping_bug(self):
         expect = DataFrame({"a": ["Y", "N", "Y"]})
         tm.assert_frame_equal(res, expect)
 
+    @pytest.mark.xfail(
+        using_pyarrow_string_dtype(), reason="can't set float into string"
+    )
     def test_replace_period(self):
         d = {
             "fname": {
@@ -1096,6 +1165,9 @@ def test_replace_period(self):
             result = df.replace(d)
         tm.assert_frame_equal(result, expected)
 
+    @pytest.mark.xfail(
+        using_pyarrow_string_dtype(), reason="can't set float into string"
+    )
     def test_replace_datetime(self):
         d = {
             "fname": {
@@ -1321,6 +1393,9 @@ def test_replace_commutative(self, df, to_replace, exp):
         result = df.replace(to_replace)
         tm.assert_frame_equal(result, expected)
 
+    @pytest.mark.xfail(
+        using_pyarrow_string_dtype(), reason="can't set float into string"
+    )
     @pytest.mark.parametrize(
         "replacer",
         [
@@ -1491,10 +1566,12 @@ def test_replace_with_compiled_regex(self):
         expected = DataFrame(["z", "b", "c"])
         tm.assert_frame_equal(result, expected)
 
-    def test_replace_intervals(self):
+    def test_replace_intervals(self, using_infer_string):
         # https://github.com/pandas-dev/pandas/issues/35931
         df = DataFrame({"a": [pd.Interval(0, 1), pd.Interval(0, 1)]})
-        result = df.replace({"a": {pd.Interval(0, 1): "x"}})
+        warning = FutureWarning if using_infer_string else None
+        with tm.assert_produces_warning(warning, match="Downcasting"):
+            result = df.replace({"a": {pd.Interval(0, 1): "x"}})
         expected = DataFrame({"a": ["x", "x"]})
         tm.assert_frame_equal(result, expected)
 
@@ -1595,6 +1672,9 @@ def test_regex_replace_scalar(
         expected.loc[expected["a"] == ".", "a"] = expected_replace_val
         tm.assert_frame_equal(result, expected)
 
+    @pytest.mark.xfail(
+        using_pyarrow_string_dtype(), reason="can't set float into string"
+    )
     @pytest.mark.parametrize("regex", [False, True])
     def test_replace_regex_dtype_frame(self, regex):
         # GH-48644
@@ -1632,9 +1712,15 @@ def test_replace_categorical_no_replacement(self):
         result = df.replace(to_replace=[".", "def"], value=["_", None])
         tm.assert_frame_equal(result, expected)
 
-    def test_replace_object_splitting(self):
+    def test_replace_object_splitting(self, using_infer_string):
         # GH#53977
         df = DataFrame({"a": ["a"], "b": "b"})
-        assert len(df._mgr.blocks) == 1
+        if using_infer_string:
+            assert len(df._mgr.blocks) == 2
+        else:
+            assert len(df._mgr.blocks) == 1
         df.replace(to_replace=r"^\s*$", value="", inplace=True, regex=True)
-        assert len(df._mgr.blocks) == 1
+        if using_infer_string:
+            assert len(df._mgr.blocks) == 2
+        else:
+            assert len(df._mgr.blocks) == 1
diff --git a/pandas/tests/frame/methods/test_reset_index.py b/pandas/tests/frame/methods/test_reset_index.py
index 20f0dcc816408..fbf36dbc4fb02 100644
--- a/pandas/tests/frame/methods/test_reset_index.py
+++ b/pandas/tests/frame/methods/test_reset_index.py
@@ -654,10 +654,14 @@ def test_rest_index_multiindex_categorical_with_missing_values(self, codes):
         ),
     ],
 )
-def test_reset_index_dtypes_on_empty_frame_with_multiindex(array, dtype):
+def test_reset_index_dtypes_on_empty_frame_with_multiindex(
+    array, dtype, using_infer_string
+):
     # GH 19602 - Preserve dtype on empty DataFrame with MultiIndex
     idx = MultiIndex.from_product([[0, 1], [0.5, 1.0], array])
     result = DataFrame(index=idx)[:0].reset_index().dtypes
+    if using_infer_string and dtype == object:
+        dtype = "string"
     expected = Series({"level_0": np.int64, "level_1": np.float64, "level_2": dtype})
     tm.assert_series_equal(result, expected)
 
@@ -676,7 +680,9 @@ def test_reset_index_empty_frame_with_datetime64_multiindex():
     tm.assert_frame_equal(result, expected)
 
 
-def test_reset_index_empty_frame_with_datetime64_multiindex_from_groupby():
+def test_reset_index_empty_frame_with_datetime64_multiindex_from_groupby(
+    using_infer_string,
+):
     # https://github.com/pandas-dev/pandas/issues/35657
     dti = pd.DatetimeIndex(["2020-01-01"], dtype="M8[ns]")
     df = DataFrame({"c1": [10.0], "c2": ["a"], "c3": dti})
@@ -687,6 +693,8 @@ def test_reset_index_empty_frame_with_datetime64_multiindex_from_groupby():
     )
     expected["c3"] = expected["c3"].astype("datetime64[ns]")
     expected["c1"] = expected["c1"].astype("float64")
+    if using_infer_string:
+        expected["c2"] = expected["c2"].astype("string[pyarrow_numpy]")
     tm.assert_frame_equal(result, expected)
 
 
diff --git a/pandas/tests/frame/methods/test_select_dtypes.py b/pandas/tests/frame/methods/test_select_dtypes.py
index e2759c5d5b7b7..47c479faed1ef 100644
--- a/pandas/tests/frame/methods/test_select_dtypes.py
+++ b/pandas/tests/frame/methods/test_select_dtypes.py
@@ -282,7 +282,7 @@ def test_select_dtypes_duplicate_columns(self):
         result = df.select_dtypes(include=[np.number], exclude=["floating"])
         tm.assert_frame_equal(result, expected)
 
-    def test_select_dtypes_not_an_attr_but_still_valid_dtype(self):
+    def test_select_dtypes_not_an_attr_but_still_valid_dtype(self, using_infer_string):
         df = DataFrame(
             {
                 "a": list("abc"),
@@ -296,11 +296,17 @@ def test_select_dtypes_not_an_attr_but_still_valid_dtype(self):
         df["g"] = df.f.diff()
         assert not hasattr(np, "u8")
         r = df.select_dtypes(include=["i8", "O"], exclude=["timedelta"])
-        e = df[["a", "b"]]
+        if using_infer_string:
+            e = df[["b"]]
+        else:
+            e = df[["a", "b"]]
         tm.assert_frame_equal(r, e)
 
         r = df.select_dtypes(include=["i8", "O", "timedelta64[ns]"])
-        e = df[["a", "b", "g"]]
+        if using_infer_string:
+            e = df[["b", "g"]]
+        else:
+            e = df[["a", "b", "g"]]
         tm.assert_frame_equal(r, e)
 
     def test_select_dtypes_empty(self):
diff --git a/pandas/tests/frame/methods/test_to_csv.py b/pandas/tests/frame/methods/test_to_csv.py
index 97fbe597d1dab..250567eafc670 100644
--- a/pandas/tests/frame/methods/test_to_csv.py
+++ b/pandas/tests/frame/methods/test_to_csv.py
@@ -682,7 +682,7 @@ def _make_frame(names=None):
             tm.assert_index_equal(recons.columns, exp.columns)
             assert len(recons) == 0
 
-    def test_to_csv_interval_index(self):
+    def test_to_csv_interval_index(self, using_infer_string):
         # GH 28210
         df = DataFrame({"A": list("abc"), "B": range(3)}, index=pd.interval_range(0, 3))
 
@@ -692,7 +692,10 @@ def test_to_csv_interval_index(self):
 
             # can't roundtrip intervalindex via read_csv so check string repr (GH 23595)
             expected = df.copy()
-            expected.index = expected.index.astype(str)
+            if using_infer_string:
+                expected.index = expected.index.astype("string[pyarrow_numpy]")
+            else:
+                expected.index = expected.index.astype(str)
 
             tm.assert_frame_equal(result, expected)
 
diff --git a/pandas/tests/frame/methods/test_update.py b/pandas/tests/frame/methods/test_update.py
index c79a37b5b30f0..7c7a0d23ff75f 100644
--- a/pandas/tests/frame/methods/test_update.py
+++ b/pandas/tests/frame/methods/test_update.py
@@ -166,11 +166,19 @@ def test_update_with_different_dtype(self, using_copy_on_write):
             with tm.assert_produces_warning(FutureWarning, match="incompatible dtype"):
                 df["c"].update(Series(["foo"], index=[0]))
 
-        expected = DataFrame({"a": [1, 3], "b": [np.nan, 2], "c": ["foo", np.nan]})
+        expected = DataFrame(
+            {
+                "a": [1, 3],
+                "b": [np.nan, 2],
+                "c": Series(["foo", np.nan], dtype="object"),
+            }
+        )
         tm.assert_frame_equal(df, expected)
 
     @td.skip_array_manager_invalid_test
-    def test_update_modify_view(self, using_copy_on_write, warn_copy_on_write):
+    def test_update_modify_view(
+        self, using_copy_on_write, warn_copy_on_write, using_infer_string
+    ):
         # GH#47188
         df = DataFrame({"A": ["1", np.nan], "B": ["100", np.nan]})
         df2 = DataFrame({"A": ["a", "x"], "B": ["100", "200"]})
@@ -181,7 +189,7 @@ def test_update_modify_view(self, using_copy_on_write, warn_copy_on_write):
             df2.update(df)
         expected = DataFrame({"A": ["1", "x"], "B": ["100", "200"]})
         tm.assert_frame_equal(df2, expected)
-        if using_copy_on_write:
+        if using_copy_on_write or using_infer_string:
             tm.assert_frame_equal(result_view, df2_orig)
         else:
             tm.assert_frame_equal(result_view, expected)
diff --git a/pandas/tests/frame/test_api.py b/pandas/tests/frame/test_api.py
index 2b392ddcfb44d..c7b444045a0f2 100644
--- a/pandas/tests/frame/test_api.py
+++ b/pandas/tests/frame/test_api.py
@@ -5,6 +5,7 @@
 import numpy as np
 import pytest
 
+from pandas._config import using_pyarrow_string_dtype
 from pandas._config.config import option_context
 
 import pandas as pd
@@ -112,6 +113,7 @@ def test_not_hashable(self):
         with pytest.raises(TypeError, match=msg):
             hash(empty_frame)
 
+    @pytest.mark.xfail(using_pyarrow_string_dtype(), reason="surrogates not allowed")
     def test_column_name_contains_unicode_surrogate(self):
         # GH 25509
         colname = "\ud83d"
diff --git a/pandas/tests/frame/test_arithmetic.py b/pandas/tests/frame/test_arithmetic.py
index a4825c80ee815..ec3222efab5a8 100644
--- a/pandas/tests/frame/test_arithmetic.py
+++ b/pandas/tests/frame/test_arithmetic.py
@@ -11,6 +11,8 @@
 import numpy as np
 import pytest
 
+from pandas._config import using_pyarrow_string_dtype
+
 import pandas.util._test_decorators as td
 
 import pandas as pd
@@ -251,6 +253,9 @@ def test_timestamp_compare(self, left, right):
             with pytest.raises(TypeError, match=msg):
                 right_f(pd.Timestamp("nat"), df)
 
+    @pytest.mark.xfail(
+        using_pyarrow_string_dtype(), reason="can't compare string and int"
+    )
     def test_mixed_comparison(self):
         # GH#13128, GH#22163 != datetime64 vs non-dt64 should be False,
         # not raise TypeError
@@ -432,8 +437,8 @@ def test_bool_flex_frame_complex_dtype(self):
 
     def test_bool_flex_frame_object_dtype(self):
         # corner, dtype=object
-        df1 = DataFrame({"col": ["foo", np.nan, "bar"]})
-        df2 = DataFrame({"col": ["foo", datetime.now(), "bar"]})
+        df1 = DataFrame({"col": ["foo", np.nan, "bar"]}, dtype=object)
+        df2 = DataFrame({"col": ["foo", datetime.now(), "bar"]}, dtype=object)
         result = df1.ne(df2)
         exp = DataFrame({"col": [False, True, False]})
         tm.assert_frame_equal(result, exp)
@@ -1976,7 +1981,12 @@ def test_dataframe_blockwise_slicelike():
     "df, col_dtype",
     [
         (DataFrame([[1.0, 2.0], [4.0, 5.0]], columns=list("ab")), "float64"),
-        (DataFrame([[1.0, "b"], [4.0, "b"]], columns=list("ab")), "object"),
+        (
+            DataFrame([[1.0, "b"], [4.0, "b"]], columns=list("ab")).astype(
+                {"b": object}
+            ),
+            "object",
+        ),
     ],
 )
 def test_dataframe_operation_with_non_numeric_types(df, col_dtype):
diff --git a/pandas/tests/frame/test_block_internals.py b/pandas/tests/frame/test_block_internals.py
index b132f136e9741..712494ef15f97 100644
--- a/pandas/tests/frame/test_block_internals.py
+++ b/pandas/tests/frame/test_block_internals.py
@@ -183,7 +183,7 @@ def test_constructor_with_convert(self):
         )
         tm.assert_series_equal(result, expected)
 
-    def test_construction_with_mixed(self, float_string_frame):
+    def test_construction_with_mixed(self, float_string_frame, using_infer_string):
         # test construction edge cases with mixed types
 
         # f7u12, this does not work without extensive workaround
@@ -206,7 +206,7 @@ def test_construction_with_mixed(self, float_string_frame):
         expected = Series(
             [np.dtype("float64")] * 4
             + [
-                np.dtype("object"),
+                np.dtype("object") if not using_infer_string else "string",
                 np.dtype("datetime64[us]"),
                 np.dtype("timedelta64[us]"),
             ],
diff --git a/pandas/tests/frame/test_constructors.py b/pandas/tests/frame/test_constructors.py
index c6fe3a154905c..e1abd0344e356 100644
--- a/pandas/tests/frame/test_constructors.py
+++ b/pandas/tests/frame/test_constructors.py
@@ -21,6 +21,8 @@
 import pytest
 import pytz
 
+from pandas._config import using_pyarrow_string_dtype
+
 from pandas._libs import lib
 from pandas.errors import IntCastingNaNError
 import pandas.util._test_decorators as td
@@ -79,7 +81,7 @@ def test_constructor_from_ndarray_with_str_dtype(self):
         #  with an array of strings each of which is e.g. "[0 1 2]"
         arr = np.arange(12).reshape(4, 3)
         df = DataFrame(arr, dtype=str)
-        expected = DataFrame(arr.astype(str))
+        expected = DataFrame(arr.astype(str), dtype=object)
         tm.assert_frame_equal(df, expected)
 
     def test_constructor_from_2d_datetimearray(self, using_array_manager):
@@ -261,8 +263,9 @@ def test_emptylike_constructor(self, emptylike, expected_index, expected_columns
         result = DataFrame(emptylike)
         tm.assert_frame_equal(result, expected)
 
-    def test_constructor_mixed(self, float_string_frame):
-        assert float_string_frame["foo"].dtype == np.object_
+    def test_constructor_mixed(self, float_string_frame, using_infer_string):
+        dtype = "string" if using_infer_string else np.object_
+        assert float_string_frame["foo"].dtype == dtype
 
     def test_constructor_cast_failure(self):
         # as of 2.0, we raise if we can't respect "dtype", previously we
@@ -323,6 +326,7 @@ def test_constructor_dtype_nocast_view_2d_array(
             assert df2._mgr.arrays[0].flags.c_contiguous
 
     @td.skip_array_manager_invalid_test
+    @pytest.mark.xfail(using_pyarrow_string_dtype(), reason="conversion copies")
     def test_1d_object_array_does_not_copy(self):
         # https://github.com/pandas-dev/pandas/issues/39272
         arr = np.array(["a", "b"], dtype="object")
@@ -330,6 +334,7 @@ def test_1d_object_array_does_not_copy(self):
         assert np.shares_memory(df.values, arr)
 
     @td.skip_array_manager_invalid_test
+    @pytest.mark.xfail(using_pyarrow_string_dtype(), reason="conversion copies")
     def test_2d_object_array_does_not_copy(self):
         # https://github.com/pandas-dev/pandas/issues/39272
         arr = np.array([["a", "b"], ["c", "d"]], dtype="object")
@@ -773,7 +778,7 @@ def test_constructor_dict_block(self):
         )
         tm.assert_numpy_array_equal(df.values, expected)
 
-    def test_constructor_dict_cast(self):
+    def test_constructor_dict_cast(self, using_infer_string):
         # cast float tests
         test_data = {"A": {"1": 1, "2": 2}, "B": {"1": "1", "2": "2", "3": "3"}}
         frame = DataFrame(test_data, dtype=float)
@@ -783,7 +788,7 @@ def test_constructor_dict_cast(self):
 
         frame = DataFrame(test_data)
         assert len(frame) == 3
-        assert frame["B"].dtype == np.object_
+        assert frame["B"].dtype == np.object_ if not using_infer_string else "string"
         assert frame["A"].dtype == np.float64
 
     def test_constructor_dict_cast2(self):
@@ -1195,7 +1200,7 @@ def test_constructor_dtype_nullable_extension_arrays(
         df = DataFrame({"a": data}, dtype=input_dtype)
         assert df["a"].dtype == expected_dtype()
 
-    def test_constructor_scalar_inference(self):
+    def test_constructor_scalar_inference(self, using_infer_string):
         data = {"int": 1, "bool": True, "float": 3.0, "complex": 4j, "object": "foo"}
         df = DataFrame(data, index=np.arange(10))
 
@@ -1203,7 +1208,7 @@ def test_constructor_scalar_inference(self):
         assert df["bool"].dtype == np.bool_
         assert df["float"].dtype == np.float64
         assert df["complex"].dtype == np.complex128
-        assert df["object"].dtype == np.object_
+        assert df["object"].dtype == np.object_ if not using_infer_string else "string"
 
     def test_constructor_arrays_and_scalars(self):
         df = DataFrame({"a": np.random.default_rng(2).standard_normal(10), "b": True})
@@ -1282,11 +1287,11 @@ def empty_gen():
         df = DataFrame(empty_gen(), columns=["A", "B"])
         tm.assert_frame_equal(df, expected)
 
-    def test_constructor_list_of_lists(self):
+    def test_constructor_list_of_lists(self, using_infer_string):
         # GH #484
         df = DataFrame(data=[[1, "a"], [2, "b"]], columns=["num", "str"])
         assert is_integer_dtype(df["num"])
-        assert df["str"].dtype == np.object_
+        assert df["str"].dtype == np.object_ if not using_infer_string else "string"
 
         # GH 4851
         # list of 0-dim ndarrays
@@ -1835,7 +1840,7 @@ def test_constructor_single_value(self):
         with pytest.raises(TypeError, match=msg):
             DataFrame("a", [1, 2], ["a", "c"], float)
 
-    def test_constructor_with_datetimes(self):
+    def test_constructor_with_datetimes(self, using_infer_string):
         intname = np.dtype(int).name
         floatname = np.dtype(np.float64).name
         objectname = np.dtype(np.object_).name
@@ -1854,7 +1859,7 @@ def test_constructor_with_datetimes(self):
         result = df.dtypes
         expected = Series(
             [np.dtype("int64")]
-            + [np.dtype(objectname)] * 2
+            + [np.dtype(objectname) if not using_infer_string else "string"] * 2
             + [np.dtype("M8[s]"), np.dtype("M8[us]")],
             index=list("ABCDE"),
         )
@@ -1876,7 +1881,7 @@ def test_constructor_with_datetimes(self):
         expected = Series(
             [np.dtype("float64")]
             + [np.dtype("int64")]
-            + [np.dtype("object")]
+            + [np.dtype("object") if not using_infer_string else "string"]
             + [np.dtype("float64")]
             + [np.dtype(intname)],
             index=["a", "b", "c", floatname, intname],
@@ -1898,7 +1903,7 @@ def test_constructor_with_datetimes(self):
         expected = Series(
             [np.dtype("float64")]
             + [np.dtype("int64")]
-            + [np.dtype("object")]
+            + [np.dtype("object") if not using_infer_string else "string"]
             + [np.dtype("float64")]
             + [np.dtype(intname)],
             index=["a", "b", "c", floatname, intname],
@@ -1935,13 +1940,13 @@ def test_constructor_with_datetimes3(self):
         df = DataFrame({"End Date": dt}, index=[0])
         assert df.iat[0, 0] == dt
         tm.assert_series_equal(
-            df.dtypes, Series({"End Date": "datetime64[us, US/Eastern]"})
+            df.dtypes, Series({"End Date": "datetime64[us, US/Eastern]"}, dtype=object)
         )
 
         df = DataFrame([{"End Date": dt}])
         assert df.iat[0, 0] == dt
         tm.assert_series_equal(
-            df.dtypes, Series({"End Date": "datetime64[ns, US/Eastern]"})
+            df.dtypes, Series({"End Date": "datetime64[ns, US/Eastern]"}, dtype=object)
         )
 
     def test_constructor_with_datetimes4(self):
@@ -2066,7 +2071,7 @@ def test_constructor_timedelta_non_ns(self, order, unit):
         #  dtype=exp_dtype.
         tm.assert_frame_equal(df, expected)
 
-    def test_constructor_for_list_with_dtypes(self):
+    def test_constructor_for_list_with_dtypes(self, using_infer_string):
         # test list of lists/ndarrays
         df = DataFrame([np.arange(5) for x in range(5)])
         result = df.dtypes
@@ -2117,7 +2122,7 @@ def test_constructor_for_list_with_dtypes(self):
             [
                 np.dtype("int64"),
                 np.dtype("float64"),
-                np.dtype("object"),
+                np.dtype("object") if not using_infer_string else "string",
                 np.dtype("datetime64[ns]"),
                 np.dtype("float64"),
             ],
diff --git a/pandas/tests/frame/test_logical_ops.py b/pandas/tests/frame/test_logical_ops.py
index a15d7d7f93f01..16ca3a202f1e0 100644
--- a/pandas/tests/frame/test_logical_ops.py
+++ b/pandas/tests/frame/test_logical_ops.py
@@ -96,7 +96,7 @@ def test_logical_ops_int_frame(self):
         res_ser = df1a_int["A"] | df1a_bool["A"]
         tm.assert_series_equal(res_ser, df1a_bool["A"])
 
-    def test_logical_ops_invalid(self):
+    def test_logical_ops_invalid(self, using_infer_string):
         # GH#5808
 
         df1 = DataFrame(1.0, index=[1], columns=["A"])
@@ -108,8 +108,14 @@ def test_logical_ops_invalid(self):
         df1 = DataFrame("foo", index=[1], columns=["A"])
         df2 = DataFrame(True, index=[1], columns=["A"])
         msg = re.escape("unsupported operand type(s) for |: 'str' and 'bool'")
-        with pytest.raises(TypeError, match=msg):
-            df1 | df2
+        if using_infer_string:
+            import pyarrow as pa
+
+            with pytest.raises(pa.lib.ArrowNotImplementedError, match="|has no kernel"):
+                df1 | df2
+        else:
+            with pytest.raises(TypeError, match=msg):
+                df1 | df2
 
     def test_logical_operators(self):
         def _check_bin_op(op):
diff --git a/pandas/tests/frame/test_query_eval.py b/pandas/tests/frame/test_query_eval.py
index 6353546648156..a498296e09c52 100644
--- a/pandas/tests/frame/test_query_eval.py
+++ b/pandas/tests/frame/test_query_eval.py
@@ -1035,7 +1035,7 @@ def test_query_with_string_columns(self, parser, engine):
             with pytest.raises(NotImplementedError, match=msg):
                 df.query("a in b and c < d", parser=parser, engine=engine)
 
-    def test_object_array_eq_ne(self, parser, engine):
+    def test_object_array_eq_ne(self, parser, engine, using_infer_string):
         df = DataFrame(
             {
                 "a": list("aaaabbbbcccc"),
@@ -1044,11 +1044,14 @@ def test_object_array_eq_ne(self, parser, engine):
                 "d": np.random.default_rng(2).integers(9, size=12),
             }
         )
-        res = df.query("a == b", parser=parser, engine=engine)
+        warning = RuntimeWarning if using_infer_string and engine == "numexpr" else None
+        with tm.assert_produces_warning(warning):
+            res = df.query("a == b", parser=parser, engine=engine)
         exp = df[df.a == df.b]
         tm.assert_frame_equal(res, exp)
 
-        res = df.query("a != b", parser=parser, engine=engine)
+        with tm.assert_produces_warning(warning):
+            res = df.query("a != b", parser=parser, engine=engine)
         exp = df[df.a != df.b]
         tm.assert_frame_equal(res, exp)
 
@@ -1087,12 +1090,16 @@ def test_query_with_nested_special_character(self, parser, engine):
             [">=", operator.ge],
         ],
     )
-    def test_query_lex_compare_strings(self, parser, engine, op, func):
+    def test_query_lex_compare_strings(
+        self, parser, engine, op, func, using_infer_string
+    ):
         a = Series(np.random.default_rng(2).choice(list("abcde"), 20))
         b = Series(np.arange(a.size))
         df = DataFrame({"X": a, "Y": b})
 
-        res = df.query(f'X {op} "d"', engine=engine, parser=parser)
+        warning = RuntimeWarning if using_infer_string and engine == "numexpr" else None
+        with tm.assert_produces_warning(warning):
+            res = df.query(f'X {op} "d"', engine=engine, parser=parser)
         expected = df[func(df.X, "d")]
         tm.assert_frame_equal(res, expected)
 
@@ -1166,7 +1173,7 @@ def test_bool_arith_expr(self, frame, parser, engine):
     @pytest.mark.parametrize("op", ["+", "-", "*", "/"])
     def test_invalid_type_for_operator_raises(self, parser, engine, op):
         df = DataFrame({"a": [1, 2], "b": ["c", "d"]})
-        msg = r"unsupported operand type\(s\) for .+: '.+' and '.+'"
+        msg = r"unsupported operand type\(s\) for .+: '.+' and '.+'|Cannot"
 
         with pytest.raises(TypeError, match=msg):
             df.eval(f"a {op} b", engine=engine, parser=parser)
diff --git a/pandas/tests/frame/test_reductions.py b/pandas/tests/frame/test_reductions.py
index 3b1a751a738f9..66145c32c18d7 100644
--- a/pandas/tests/frame/test_reductions.py
+++ b/pandas/tests/frame/test_reductions.py
@@ -6,6 +6,8 @@
 import numpy as np
 import pytest
 
+from pandas._config import using_pyarrow_string_dtype
+
 from pandas.compat import (
     IS64,
     is_platform_windows,
@@ -243,11 +245,17 @@ class TestDataFrameAnalytics:
             pytest.param("kurt", marks=td.skip_if_no("scipy")),
         ],
     )
-    def test_stat_op_api_float_string_frame(self, float_string_frame, axis, opname):
-        if (opname in ("sum", "min", "max") and axis == 0) or opname in (
-            "count",
-            "nunique",
-        ):
+    def test_stat_op_api_float_string_frame(
+        self, float_string_frame, axis, opname, using_infer_string
+    ):
+        if (
+            (opname in ("sum", "min", "max") and axis == 0)
+            or opname
+            in (
+                "count",
+                "nunique",
+            )
+        ) and not (using_infer_string and opname == "sum"):
             getattr(float_string_frame, opname)(axis=axis)
         else:
             if opname in ["var", "std", "sem", "skew", "kurt"]:
@@ -273,7 +281,11 @@ def test_stat_op_api_float_string_frame(self, float_string_frame, axis, opname):
             elif opname in ["min", "max"]:
                 msg = "'[><]=' not supported between instances of 'float' and 'str'"
             elif opname == "median":
-                msg = re.compile(r"Cannot convert \[.*\] to numeric", flags=re.S)
+                msg = re.compile(
+                    r"Cannot convert \[.*\] to numeric|does not support", flags=re.S
+                )
+            if not isinstance(msg, re.Pattern):
+                msg = msg + "|does not support"
             with pytest.raises(TypeError, match=msg):
                 getattr(float_string_frame, opname)(axis=axis)
         if opname != "nunique":
@@ -434,6 +446,7 @@ def test_mixed_ops(self, op):
                 "Could not convert",
                 "could not convert",
                 "can't multiply sequence by non-int",
+                "does not support",
             ]
         )
         with pytest.raises(TypeError, match=msg):
@@ -445,11 +458,15 @@ def test_mixed_ops(self, op):
                     "Could not convert",
                     "could not convert",
                     "can't multiply sequence by non-int",
+                    "does not support",
                 ]
             )
             with pytest.raises(TypeError, match=msg):
                 getattr(df, op)()
 
+    @pytest.mark.xfail(
+        using_pyarrow_string_dtype(), reason="sum doesn't work for arrow strings"
+    )
     def test_reduce_mixed_frame(self):
         # GH 6806
         df = DataFrame(
@@ -516,7 +533,9 @@ def test_mean_mixed_string_decimal(self):
 
         df = DataFrame(d)
 
-        with pytest.raises(TypeError, match="unsupported operand type"):
+        with pytest.raises(
+            TypeError, match="unsupported operand type|does not support"
+        ):
             df.mean()
         result = df[["A", "C"]].mean()
         expected = Series([2.7, 681.6], index=["A", "C"], dtype=object)
@@ -652,7 +671,7 @@ def test_mode_dropna(self, dropna, expected):
                 "A": [12, 12, 19, 11],
                 "B": [10, 10, np.nan, 3],
                 "C": [1, np.nan, np.nan, np.nan],
-                "D": [np.nan, np.nan, "a", np.nan],
+                "D": Series([np.nan, np.nan, "a", np.nan], dtype=object),
                 "E": Categorical([np.nan, np.nan, "a", np.nan]),
                 "F": DatetimeIndex(["NaT", "2000-01-02", "NaT", "NaT"], dtype="M8[ns]"),
                 "G": to_timedelta(["1 days", "nan", "nan", "nan"]),
@@ -672,14 +691,15 @@ def test_mode_dropna(self, dropna, expected):
         expected = DataFrame(expected)
         tm.assert_frame_equal(result, expected)
 
-    def test_mode_sortwarning(self):
+    def test_mode_sortwarning(self, using_infer_string):
         # Check for the warning that is raised when the mode
         # results cannot be sorted
 
         df = DataFrame({"A": [np.nan, np.nan, "a", "a"]})
         expected = DataFrame({"A": ["a", np.nan]})
 
-        with tm.assert_produces_warning(UserWarning):
+        warning = None if using_infer_string else UserWarning
+        with tm.assert_produces_warning(warning):
             result = df.mode(dropna=False)
             result = result.sort_values(by="A").reset_index(drop=True)
 
@@ -969,7 +989,8 @@ def test_sum_mixed_datetime(self):
 
     def test_mean_corner(self, float_frame, float_string_frame):
         # unit test when have object data
-        with pytest.raises(TypeError, match="Could not convert"):
+        msg = "Could not convert|does not support"
+        with pytest.raises(TypeError, match=msg):
             float_string_frame.mean(axis=0)
 
         # xs sum mixed type, just want to know it works...
@@ -1341,7 +1362,9 @@ def test_any_all_extra(self):
     @pytest.mark.parametrize("axis", [0, 1])
     @pytest.mark.parametrize("bool_agg_func", ["any", "all"])
     @pytest.mark.parametrize("skipna", [True, False])
-    def test_any_all_object_dtype(self, axis, bool_agg_func, skipna):
+    def test_any_all_object_dtype(
+        self, axis, bool_agg_func, skipna, using_infer_string
+    ):
         # GH#35450
         df = DataFrame(
             data=[
@@ -1351,8 +1374,13 @@ def test_any_all_object_dtype(self, axis, bool_agg_func, skipna):
                 [np.nan, np.nan, "5", np.nan],
             ]
         )
+        if using_infer_string:
+            # na in object is True while in string pyarrow numpy it's false
+            val = not axis == 0 and not skipna and bool_agg_func == "all"
+        else:
+            val = True
         result = getattr(df, bool_agg_func)(axis=axis, skipna=skipna)
-        expected = Series([True, True, True, True])
+        expected = Series([True, True, val, True])
         tm.assert_series_equal(result, expected)
 
     # GH#50947 deprecates this but it is not emitting a warning in some builds.
@@ -1378,7 +1406,8 @@ def test_any_datetime(self):
     def test_any_all_bool_only(self):
         # GH 25101
         df = DataFrame(
-            {"col1": [1, 2, 3], "col2": [4, 5, 6], "col3": [None, None, None]}
+            {"col1": [1, 2, 3], "col2": [4, 5, 6], "col3": [None, None, None]},
+            columns=Index(["col1", "col2", "col3"], dtype=object),
         )
 
         result = df.all(bool_only=True)
@@ -1931,6 +1960,9 @@ def test_sum_timedelta64_skipna_false(using_array_manager, request):
     tm.assert_series_equal(result, expected)
 
 
+@pytest.mark.xfail(
+    using_pyarrow_string_dtype(), reason="sum doesn't work with arrow strings"
+)
 def test_mixed_frame_with_integer_sum():
     # https://github.com/pandas-dev/pandas/issues/34520
     df = DataFrame([["a", 1]], columns=list("ab"))
@@ -1951,7 +1983,7 @@ def test_minmax_extensionarray(method, numeric_only):
     expected = Series(
         [getattr(int64_info, method)],
         dtype="Int64",
-        index=Index(["Int64"], dtype="object"),
+        index=Index(["Int64"]),
     )
     tm.assert_series_equal(result, expected)
 
@@ -1969,7 +2001,7 @@ def test_prod_sum_min_count_mixed_object():
     df = DataFrame([1, "a", True])
 
     result = df.prod(axis=0, min_count=1, numeric_only=False)
-    expected = Series(["a"])
+    expected = Series(["a"], dtype=object)
     tm.assert_series_equal(result, expected)
 
     msg = re.escape("unsupported operand type(s) for +: 'int' and 'str'")
diff --git a/pandas/tests/frame/test_repr.py b/pandas/tests/frame/test_repr.py
index 6184e791cab5d..776007fb9691d 100644
--- a/pandas/tests/frame/test_repr.py
+++ b/pandas/tests/frame/test_repr.py
@@ -7,6 +7,8 @@
 import numpy as np
 import pytest
 
+from pandas._config import using_pyarrow_string_dtype
+
 from pandas import (
     NA,
     Categorical,
@@ -174,6 +176,7 @@ def test_repr_mixed_big(self):
 
         repr(biggie)
 
+    @pytest.mark.xfail(using_pyarrow_string_dtype(), reason="/r in")
     def test_repr(self):
         # columns but no index
         no_index = DataFrame(columns=[0, 1, 3])
diff --git a/pandas/tests/frame/test_stack_unstack.py b/pandas/tests/frame/test_stack_unstack.py
index 2e7e8eba270c0..554a9d4ce2d5d 100644
--- a/pandas/tests/frame/test_stack_unstack.py
+++ b/pandas/tests/frame/test_stack_unstack.py
@@ -619,7 +619,7 @@ def test_unstack_to_series(self, float_frame):
             data = data.unstack()
         tm.assert_frame_equal(old_data, data)
 
-    def test_unstack_dtypes(self):
+    def test_unstack_dtypes(self, using_infer_string):
         # GH 2929
         rows = [[1, 1, 3, 4], [1, 2, 3, 4], [2, 1, 3, 4], [2, 2, 3, 4]]
 
@@ -655,8 +655,9 @@ def test_unstack_dtypes(self):
         df2["D"] = "foo"
         df3 = df2.unstack("B")
         result = df3.dtypes
+        dtype = "string" if using_infer_string else np.dtype("object")
         expected = Series(
-            [np.dtype("float64")] * 2 + [np.dtype("object")] * 2,
+            [np.dtype("float64")] * 2 + [dtype] * 2,
             index=MultiIndex.from_arrays(
                 [["C", "C", "D", "D"], [1, 2, 1, 2]], names=(None, "B")
             ),
@@ -1359,14 +1360,16 @@ def test_unstack_fill_frame_object():
     # By default missing values will be NaN
     result = data.unstack()
     expected = DataFrame(
-        {"a": ["a", np.nan, "a"], "b": ["b", "c", np.nan]}, index=list("xyz")
+        {"a": ["a", np.nan, "a"], "b": ["b", "c", np.nan]},
+        index=list("xyz"),
+        dtype=object,
     )
     tm.assert_frame_equal(result, expected)
 
     # Fill with any value replaces missing values as expected
     result = data.unstack(fill_value="d")
     expected = DataFrame(
-        {"a": ["a", "d", "a"], "b": ["b", "c", "d"]}, index=list("xyz")
+        {"a": ["a", "d", "a"], "b": ["b", "c", "d"]}, index=list("xyz"), dtype=object
     )
     tm.assert_frame_equal(result, expected)
 
@@ -2083,7 +2086,7 @@ def test_stack_multiple_bug(self, future_stack):
         multi = df.set_index(["DATE", "ID"])
         multi.columns.name = "Params"
         unst = multi.unstack("ID")
-        msg = re.escape("agg function failed [how->mean,dtype->object]")
+        msg = re.escape("agg function failed [how->mean,dtype->")
         with pytest.raises(TypeError, match=msg):
             unst.resample("W-THU").mean()
         down = unst.resample("W-THU").mean(numeric_only=True)
@@ -2298,7 +2301,7 @@ def test_stack_unstack_unordered_multiindex(self, future_stack):
         tm.assert_frame_equal(result, expected)
 
     def test_unstack_preserve_types(
-        self, multiindex_year_month_day_dataframe_random_data
+        self, multiindex_year_month_day_dataframe_random_data, using_infer_string
     ):
         # GH#403
         ymd = multiindex_year_month_day_dataframe_random_data
@@ -2307,7 +2310,11 @@ def test_unstack_preserve_types(
 
         unstacked = ymd.unstack("month")
         assert unstacked["A", 1].dtype == np.float64
-        assert unstacked["E", 1].dtype == np.object_
+        assert (
+            unstacked["E", 1].dtype == np.object_
+            if not using_infer_string
+            else "string"
+        )
         assert unstacked["F", 1].dtype == np.float64
 
     def test_unstack_group_index_overflow(self, future_stack):
@@ -2367,7 +2374,7 @@ def test_unstack_with_missing_int_cast_to_float(self, using_array_manager):
 
         expected = DataFrame(
             [[10.0, 10.0, 1.0, 1.0], [np.nan, 10.0, 0.0, 1.0]],
-            index=Index(["A", "B"], dtype="object", name="a"),
+            index=Index(["A", "B"], name="a"),
             columns=MultiIndex.from_tuples(
                 [("v", "ca"), ("v", "cb"), ("is_", "ca"), ("is_", "cb")],
                 names=[None, "b"],
diff --git a/pandas/tests/frame/test_unary.py b/pandas/tests/frame/test_unary.py
index 5e29d3c868983..850c92013694f 100644
--- a/pandas/tests/frame/test_unary.py
+++ b/pandas/tests/frame/test_unary.py
@@ -48,15 +48,25 @@ def test_neg_object(self, df, expected):
             pd.DataFrame({"a": pd.to_datetime(["2017-01-22", "1970-01-01"])}),
         ],
     )
-    def test_neg_raises(self, df):
+    def test_neg_raises(self, df, using_infer_string):
         msg = (
             "bad operand type for unary -: 'str'|"
             r"bad operand type for unary -: 'DatetimeArray'"
         )
-        with pytest.raises(TypeError, match=msg):
-            (-df)
-        with pytest.raises(TypeError, match=msg):
-            (-df["a"])
+        if using_infer_string and df.dtypes.iloc[0] == "string":
+            import pyarrow as pa
+
+            msg = "has no kernel"
+            with pytest.raises(pa.lib.ArrowNotImplementedError, match=msg):
+                (-df)
+            with pytest.raises(pa.lib.ArrowNotImplementedError, match=msg):
+                (-df["a"])
+
+        else:
+            with pytest.raises(TypeError, match=msg):
+                (-df)
+            with pytest.raises(TypeError, match=msg):
+                (-df["a"])
 
     def test_invert(self, float_frame):
         df = float_frame
diff --git a/pandas/tests/groupby/test_apply.py b/pandas/tests/groupby/test_apply.py
index 60b386adb664a..34b6e7c4cde5f 100644
--- a/pandas/tests/groupby/test_apply.py
+++ b/pandas/tests/groupby/test_apply.py
@@ -37,7 +37,7 @@ def store(group):
     tm.assert_frame_equal(groups[0], expected_value)
 
 
-def test_apply_index_date():
+def test_apply_index_date(using_infer_string):
     # GH 5788
     ts = [
         "2011-05-16 00:00",
@@ -77,7 +77,7 @@ def test_apply_index_date():
     tm.assert_frame_equal(result, expected)
 
 
-def test_apply_index_date_object():
+def test_apply_index_date_object(using_infer_string):
     # GH 5789
     # don't auto coerce dates
     ts = [
@@ -109,8 +109,9 @@ def test_apply_index_date_object():
         1.40750,
         1.40649,
     ]
+    dtype = "string[pyarrow_numpy]" if using_infer_string else object
     exp_idx = Index(
-        ["2011-05-16", "2011-05-17", "2011-05-18"], dtype=object, name="date"
+        ["2011-05-16", "2011-05-17", "2011-05-18"], dtype=dtype, name="date"
     )
     expected = Series(["00:00", "02:00", "02:00"], index=exp_idx)
     msg = "DataFrameGroupBy.apply operated on the grouping columns"
@@ -121,14 +122,15 @@ def test_apply_index_date_object():
     tm.assert_series_equal(result, expected)
 
 
-def test_apply_trivial():
+def test_apply_trivial(using_infer_string):
     # GH 20066
     # trivial apply: ignore input and return a constant dataframe.
     df = DataFrame(
         {"key": ["a", "a", "b", "b", "a"], "data": [1.0, 2.0, 3.0, 4.0, 5.0]},
         columns=["key", "data"],
     )
-    expected = pd.concat([df.iloc[1:], df.iloc[1:]], axis=1, keys=["float64", "object"])
+    dtype = "string" if using_infer_string else "object"
+    expected = pd.concat([df.iloc[1:], df.iloc[1:]], axis=1, keys=["float64", dtype])
 
     msg = "DataFrame.groupby with axis=1 is deprecated"
     with tm.assert_produces_warning(FutureWarning, match=msg):
@@ -138,13 +140,14 @@ def test_apply_trivial():
     tm.assert_frame_equal(result, expected)
 
 
-def test_apply_trivial_fail():
+def test_apply_trivial_fail(using_infer_string):
     # GH 20066
     df = DataFrame(
         {"key": ["a", "a", "b", "b", "a"], "data": [1.0, 2.0, 3.0, 4.0, 5.0]},
         columns=["key", "data"],
     )
-    expected = pd.concat([df, df], axis=1, keys=["float64", "object"])
+    dtype = "string" if using_infer_string else "object"
+    expected = pd.concat([df, df], axis=1, keys=["float64", dtype])
     msg = "DataFrame.groupby with axis=1 is deprecated"
     with tm.assert_produces_warning(FutureWarning, match=msg):
         gb = df.groupby([str(x) for x in df.dtypes], axis=1, group_keys=True)
@@ -941,7 +944,7 @@ def test_func_returns_object():
     "group_column_dtlike",
     [datetime.today(), datetime.today().date(), datetime.today().time()],
 )
-def test_apply_datetime_issue(group_column_dtlike):
+def test_apply_datetime_issue(group_column_dtlike, using_infer_string):
     # GH-28247
     # groupby-apply throws an error if one of the columns in the DataFrame
     #   is a datetime object and the column labels are different from
@@ -952,9 +955,8 @@ def test_apply_datetime_issue(group_column_dtlike):
     with tm.assert_produces_warning(FutureWarning, match=msg):
         result = df.groupby("a").apply(lambda x: Series(["spam"], index=[42]))
 
-    expected = DataFrame(
-        ["spam"], Index(["foo"], dtype="object", name="a"), columns=[42]
-    )
+    dtype = "string" if using_infer_string else "object"
+    expected = DataFrame(["spam"], Index(["foo"], dtype=dtype, name="a"), columns=[42])
     tm.assert_frame_equal(result, expected)
 
 
@@ -1021,7 +1023,7 @@ def test_apply_multi_level_name(category):
     assert df.index.names == ["A", "B"]
 
 
-def test_groupby_apply_datetime_result_dtypes():
+def test_groupby_apply_datetime_result_dtypes(using_infer_string):
     # GH 14849
     data = DataFrame.from_records(
         [
@@ -1035,8 +1037,9 @@ def test_groupby_apply_datetime_result_dtypes():
     msg = "DataFrameGroupBy.apply operated on the grouping columns"
     with tm.assert_produces_warning(FutureWarning, match=msg):
         result = data.groupby("color").apply(lambda g: g.iloc[0]).dtypes
+    dtype = "string" if using_infer_string else object
     expected = Series(
-        [np.dtype("datetime64[ns]"), object, object, np.int64, object],
+        [np.dtype("datetime64[ns]"), dtype, dtype, np.int64, dtype],
         index=["observation", "color", "mood", "intensity", "score"],
     )
     tm.assert_series_equal(result, expected)
diff --git a/pandas/tests/groupby/test_categorical.py b/pandas/tests/groupby/test_categorical.py
index d4ccbe4c1c376..7a91601bf688f 100644
--- a/pandas/tests/groupby/test_categorical.py
+++ b/pandas/tests/groupby/test_categorical.py
@@ -82,7 +82,7 @@ def get_stats(group):
     assert result.index.names[0] == "C"
 
 
-def test_basic():  # TODO: split this test
+def test_basic(using_infer_string):  # TODO: split this test
     cats = Categorical(
         ["a", "a", "a", "b", "b", "b", "c", "c", "c"],
         categories=["a", "b", "c", "d"],
@@ -129,7 +129,8 @@ def f(x):
         result = g.apply(f)
     expected = x.iloc[[0, 1]].copy()
     expected.index = Index([1, 2], name="person_id")
-    expected["person_name"] = expected["person_name"].astype("object")
+    dtype = "string[pyarrow_numpy]" if using_infer_string else object
+    expected["person_name"] = expected["person_name"].astype(dtype)
     tm.assert_frame_equal(result, expected)
 
     # GH 9921
diff --git a/pandas/tests/groupby/test_groupby.py b/pandas/tests/groupby/test_groupby.py
index 62347ec1d3d6a..802cae9ff65f0 100644
--- a/pandas/tests/groupby/test_groupby.py
+++ b/pandas/tests/groupby/test_groupby.py
@@ -11,6 +11,8 @@
 )
 import pandas.util._test_decorators as td
 
+from pandas.core.dtypes.common import is_string_dtype
+
 import pandas as pd
 from pandas import (
     Categorical,
@@ -687,7 +689,7 @@ def test_frame_multi_key_function_list_partial_failure():
 
     grouped = data.groupby(["A", "B"])
     funcs = ["mean", "std"]
-    msg = re.escape("agg function failed [how->mean,dtype->object]")
+    msg = re.escape("agg function failed [how->mean,dtype->")
     with pytest.raises(TypeError, match=msg):
         grouped.agg(funcs)
 
@@ -980,7 +982,7 @@ def test_groupby_multi_corner(df):
 
 def test_raises_on_nuisance(df):
     grouped = df.groupby("A")
-    msg = re.escape("agg function failed [how->mean,dtype->object]")
+    msg = re.escape("agg function failed [how->mean,dtype->")
     with pytest.raises(TypeError, match=msg):
         grouped.agg("mean")
     with pytest.raises(TypeError, match=msg):
@@ -1036,7 +1038,7 @@ def test_omit_nuisance_agg(df, agg_function, numeric_only):
             msg = "could not convert string to float: 'one'"
         else:
             klass = TypeError
-            msg = re.escape(f"agg function failed [how->{agg_function},dtype->object]")
+            msg = re.escape(f"agg function failed [how->{agg_function},dtype->")
         with pytest.raises(klass, match=msg):
             getattr(grouped, agg_function)(numeric_only=numeric_only)
     else:
@@ -1061,7 +1063,7 @@ def test_raise_on_nuisance_python_single(df):
 
 def test_raise_on_nuisance_python_multiple(three_group):
     grouped = three_group.groupby(["A", "B"])
-    msg = re.escape("agg function failed [how->mean,dtype->object]")
+    msg = re.escape("agg function failed [how->mean,dtype->")
     with pytest.raises(TypeError, match=msg):
         grouped.agg("mean")
     with pytest.raises(TypeError, match=msg):
@@ -1104,7 +1106,7 @@ def test_wrap_aggregated_output_multindex(multiindex_dataframe_random_data):
     df["baz", "two"] = "peekaboo"
 
     keys = [np.array([0, 0, 1]), np.array([0, 0, 1])]
-    msg = re.escape("agg function failed [how->mean,dtype->object]")
+    msg = re.escape("agg function failed [how->mean,dtype->")
     with pytest.raises(TypeError, match=msg):
         df.groupby(keys).agg("mean")
     agged = df.drop(columns=("baz", "two")).groupby(keys).agg("mean")
@@ -1193,7 +1195,7 @@ def test_groupby_complex():
     tm.assert_series_equal(result, expected)
 
 
-def test_groupby_complex_numbers():
+def test_groupby_complex_numbers(using_infer_string):
     # GH 17927
     df = DataFrame(
         [
@@ -1202,10 +1204,11 @@ def test_groupby_complex_numbers():
             {"a": 4, "b": 1},
         ]
     )
+    dtype = "string[pyarrow_numpy]" if using_infer_string else object
     expected = DataFrame(
         np.array([1, 1, 1], dtype=np.int64),
         index=Index([(1 + 1j), (1 + 2j), (1 + 0j)], name="b"),
-        columns=Index(["a"], dtype="object"),
+        columns=Index(["a"], dtype=dtype),
     )
     result = df.groupby("b", sort=False).count()
     tm.assert_frame_equal(result, expected)
@@ -1720,14 +1723,18 @@ def g(group):
 
 
 @pytest.mark.parametrize("grouper", ["A", ["A", "B"]])
-def test_set_group_name(df, grouper):
+def test_set_group_name(df, grouper, using_infer_string):
     def f(group):
         assert group.name is not None
         return group
 
     def freduce(group):
         assert group.name is not None
-        return group.sum()
+        if using_infer_string and grouper == "A" and is_string_dtype(group.dtype):
+            with pytest.raises(TypeError, match="does not support"):
+                group.sum()
+        else:
+            return group.sum()
 
     def freducex(x):
         return freduce(x)
@@ -2024,7 +2031,9 @@ def test_pivot_table_values_key_error():
 @pytest.mark.parametrize(
     "op", ["idxmax", "idxmin", "min", "max", "sum", "prod", "skew"]
 )
-def test_empty_groupby(columns, keys, values, method, op, using_array_manager, dropna):
+def test_empty_groupby(
+    columns, keys, values, method, op, using_array_manager, dropna, using_infer_string
+):
     # GH8093 & GH26411
     override_dtype = None
 
@@ -2065,7 +2074,11 @@ def get_categorical_invalid_expected():
             # Categorical is special without 'observed=True'
             idx = Index(lev, name=keys[0])
 
-        expected = DataFrame([], columns=[], index=idx)
+        if using_infer_string:
+            columns = Index([], dtype="string[pyarrow_numpy]")
+        else:
+            columns = []
+        expected = DataFrame([], columns=columns, index=idx)
         return expected
 
     is_per = isinstance(df.dtypes.iloc[0], pd.PeriodDtype)
diff --git a/pandas/tests/groupby/test_numeric_only.py b/pandas/tests/groupby/test_numeric_only.py
index 0141adf44c86b..ff4685b1e412d 100644
--- a/pandas/tests/groupby/test_numeric_only.py
+++ b/pandas/tests/groupby/test_numeric_only.py
@@ -180,6 +180,7 @@ def _check(self, df, method, expected_columns, expected_columns_numeric):
                 [
                     "category type does not support sum operations",
                     re.escape(f"agg function failed [how->{method},dtype->object]"),
+                    re.escape(f"agg function failed [how->{method},dtype->string]"),
                 ]
             )
             with pytest.raises(exception, match=msg):
@@ -196,6 +197,7 @@ def _check(self, df, method, expected_columns, expected_columns_numeric):
                     "function is not implemented for this dtype",
                     f"Cannot perform {method} with non-ordered Categorical",
                     re.escape(f"agg function failed [how->{method},dtype->object]"),
+                    re.escape(f"agg function failed [how->{method},dtype->string]"),
                 ]
             )
             with pytest.raises(exception, match=msg):
@@ -206,7 +208,7 @@ def _check(self, df, method, expected_columns, expected_columns_numeric):
 
 
 @pytest.mark.parametrize("numeric_only", [True, False, None])
-def test_axis1_numeric_only(request, groupby_func, numeric_only):
+def test_axis1_numeric_only(request, groupby_func, numeric_only, using_infer_string):
     if groupby_func in ("idxmax", "idxmin"):
         pytest.skip("idxmax and idx_min tested in test_idxmin_idxmax_axis1")
     if groupby_func in ("corrwith", "skew"):
@@ -268,8 +270,15 @@ def test_axis1_numeric_only(request, groupby_func, numeric_only):
             "can't multiply sequence by non-int of type 'float'",
             # cumsum, diff, pct_change
             "unsupported operand type",
+            "has no kernel",
         )
-        with pytest.raises(TypeError, match=f"({'|'.join(msgs)})"):
+        if using_infer_string:
+            import pyarrow as pa
+
+            errs = (TypeError, pa.lib.ArrowNotImplementedError)
+        else:
+            errs = TypeError
+        with pytest.raises(errs, match=f"({'|'.join(msgs)})"):
             with tm.assert_produces_warning(FutureWarning, match=warn_msg):
                 method(*args, **kwargs)
     else:
diff --git a/pandas/tests/groupby/test_raises.py b/pandas/tests/groupby/test_raises.py
index 2800f08b5fd90..0b451ce73db89 100644
--- a/pandas/tests/groupby/test_raises.py
+++ b/pandas/tests/groupby/test_raises.py
@@ -189,7 +189,7 @@ def test_groupby_raises_string(
         "sum": (None, ""),
         "var": (
             TypeError,
-            re.escape("agg function failed [how->var,dtype->object]"),
+            re.escape("agg function failed [how->var,dtype->"),
         ),
     }[groupby_func]
 

From fb05cc7781637906728e95be9b418e774b0e67b2 Mon Sep 17 00:00:00 2001
From: Patrick Hoefler <61934744+phofl@users.noreply.github.com>
Date: Sat, 9 Dec 2023 20:18:22 +0100
Subject: [PATCH 12/15] BUG: read_csv not respecting object dtype when option
 is set (#56047)

* BUG: read_csv not respecting object dtype when option is set

* Update readers.py

* Cover str too

* Adjust

* Fixup

* Fixup

* Update readers.py
---
 doc/source/whatsnew/v2.1.4.rst                |  1 +
 pandas/io/parsers/arrow_parser_wrapper.py     | 14 +-----
 pandas/io/parsers/readers.py                  | 44 ++++++++++++++++++-
 .../io/parser/dtypes/test_dtypes_basic.py     | 35 +++++++++++++++
 4 files changed, 80 insertions(+), 14 deletions(-)

diff --git a/doc/source/whatsnew/v2.1.4.rst b/doc/source/whatsnew/v2.1.4.rst
index 9cc79b7090499..57b83a294963b 100644
--- a/doc/source/whatsnew/v2.1.4.rst
+++ b/doc/source/whatsnew/v2.1.4.rst
@@ -24,6 +24,7 @@ Bug fixes
 - Bug in :class:`Series` when trying to cast date-like string inputs to :class:`ArrowDtype` of ``pyarrow.timestamp`` (:issue:`56266`)
 - Bug in :class:`Timestamp` construction with ``ts_input="now"`` or ``ts_input="today"`` giving a different unit from :meth:`Timestamp.now` or :meth:`Timestamp.today` (:issue:`55879`)
 - Bug in :meth:`Index.__getitem__` returning wrong result for Arrow dtypes and negative stepsize (:issue:`55832`)
+- Fixed bug in :func:`read_csv` not respecting object dtype when ``infer_string`` option is set (:issue:`56047`)
 - Fixed bug in :func:`to_numeric` converting to extension dtype for ``string[pyarrow_numpy]`` dtype (:issue:`56179`)
 - Fixed bug in :meth:`.DataFrameGroupBy.min` and :meth:`.DataFrameGroupBy.max` not preserving extension dtype for empty object (:issue:`55619`)
 - Fixed bug in :meth:`DataFrame.__setitem__` casting :class:`Index` with object-dtype to PyArrow backed strings when ``infer_string`` option is set (:issue:`55638`)
diff --git a/pandas/io/parsers/arrow_parser_wrapper.py b/pandas/io/parsers/arrow_parser_wrapper.py
index 1c79392d54771..66a7ccacf675b 100644
--- a/pandas/io/parsers/arrow_parser_wrapper.py
+++ b/pandas/io/parsers/arrow_parser_wrapper.py
@@ -296,18 +296,8 @@ def read(self) -> DataFrame:
             dtype_mapping[pa.null()] = pd.Int64Dtype()
             frame = table.to_pandas(types_mapper=dtype_mapping.get)
         elif using_pyarrow_string_dtype():
-
-            def types_mapper(dtype):
-                dtype_dict = self.kwds["dtype"]
-                if dtype_dict is not None and dtype_dict.get(dtype, None) is not None:
-                    return dtype_dict.get(dtype)
-                return arrow_string_types_mapper()(dtype)
-
-            frame = table.to_pandas(types_mapper=types_mapper)
+            frame = table.to_pandas(types_mapper=arrow_string_types_mapper())
 
         else:
-            if isinstance(self.kwds.get("dtype"), dict):
-                frame = table.to_pandas(types_mapper=self.kwds["dtype"].get)
-            else:
-                frame = table.to_pandas()
+            frame = table.to_pandas()
         return self._finalize_pandas_output(frame)
diff --git a/pandas/io/parsers/readers.py b/pandas/io/parsers/readers.py
index 66990de6d3b89..2f9243c895ae8 100644
--- a/pandas/io/parsers/readers.py
+++ b/pandas/io/parsers/readers.py
@@ -5,7 +5,10 @@
 """
 from __future__ import annotations
 
-from collections import abc
+from collections import (
+    abc,
+    defaultdict,
+)
 import csv
 import sys
 from textwrap import fill
@@ -23,6 +26,8 @@
 
 import numpy as np
 
+from pandas._config import using_copy_on_write
+
 from pandas._libs import lib
 from pandas._libs.parsers import STR_NA_VALUES
 from pandas.errors import (
@@ -38,8 +43,10 @@
     is_float,
     is_integer,
     is_list_like,
+    pandas_dtype,
 )
 
+from pandas import Series
 from pandas.core.frame import DataFrame
 from pandas.core.indexes.api import RangeIndex
 from pandas.core.shared_docs import _shared_docs
@@ -1846,7 +1853,40 @@ def read(self, nrows: int | None = None) -> DataFrame:
             else:
                 new_rows = len(index)
 
-            df = DataFrame(col_dict, columns=columns, index=index)
+            if hasattr(self, "orig_options"):
+                dtype_arg = self.orig_options.get("dtype", None)
+            else:
+                dtype_arg = None
+
+            if isinstance(dtype_arg, dict):
+                dtype = defaultdict(lambda: None)  # type: ignore[var-annotated]
+                dtype.update(dtype_arg)
+            elif dtype_arg is not None and pandas_dtype(dtype_arg) in (
+                np.str_,
+                np.object_,
+            ):
+                dtype = defaultdict(lambda: dtype_arg)
+            else:
+                dtype = None
+
+            if dtype is not None:
+                new_col_dict = {}
+                for k, v in col_dict.items():
+                    d = (
+                        dtype[k]
+                        if pandas_dtype(dtype[k]) in (np.str_, np.object_)
+                        else None
+                    )
+                    new_col_dict[k] = Series(v, index=index, dtype=d, copy=False)
+            else:
+                new_col_dict = col_dict
+
+            df = DataFrame(
+                new_col_dict,
+                columns=columns,
+                index=index,
+                copy=not using_copy_on_write(),
+            )
 
             self._currow += new_rows
         return df
diff --git a/pandas/tests/io/parser/dtypes/test_dtypes_basic.py b/pandas/tests/io/parser/dtypes/test_dtypes_basic.py
index 0deafda750904..ce02e752fb90b 100644
--- a/pandas/tests/io/parser/dtypes/test_dtypes_basic.py
+++ b/pandas/tests/io/parser/dtypes/test_dtypes_basic.py
@@ -574,6 +574,41 @@ def test_string_inference(all_parsers):
     tm.assert_frame_equal(result, expected)
 
 
+@pytest.mark.parametrize("dtype", ["O", object, "object", np.object_, str, np.str_])
+def test_string_inference_object_dtype(all_parsers, dtype):
+    # GH#56047
+    pytest.importorskip("pyarrow")
+
+    data = """a,b
+x,a
+y,a
+z,a"""
+    parser = all_parsers
+    with pd.option_context("future.infer_string", True):
+        result = parser.read_csv(StringIO(data), dtype=dtype)
+
+    expected = DataFrame(
+        {
+            "a": pd.Series(["x", "y", "z"], dtype=object),
+            "b": pd.Series(["a", "a", "a"], dtype=object),
+        },
+        columns=pd.Index(["a", "b"], dtype="string[pyarrow_numpy]"),
+    )
+    tm.assert_frame_equal(result, expected)
+
+    with pd.option_context("future.infer_string", True):
+        result = parser.read_csv(StringIO(data), dtype={"a": dtype})
+
+    expected = DataFrame(
+        {
+            "a": pd.Series(["x", "y", "z"], dtype=object),
+            "b": pd.Series(["a", "a", "a"], dtype="string[pyarrow_numpy]"),
+        },
+        columns=pd.Index(["a", "b"], dtype="string[pyarrow_numpy]"),
+    )
+    tm.assert_frame_equal(result, expected)
+
+
 def test_accurate_parsing_of_large_integers(all_parsers):
     # GH#52505
     data = """SYMBOL,MOMENT,ID,ID_DEAL

From 91ddc8b66a0eef9312014387ce0108f1be29a3a9 Mon Sep 17 00:00:00 2001
From: Patrick Hoefler <61934744+phofl@users.noreply.github.com>
Date: Sat, 9 Dec 2023 20:20:50 +0100
Subject: [PATCH 13/15] Adjust Index specific tests for string option (#56074)

* BUG: setitem casting object Index to arrow strings

* Fix

* Start fixing index tests

* BUG: Index.isin raising for arrow strings and null set

* Fix more tests

* TST: Fix shares_memory for arrow string dtype

* TST: Fix shares_memory for arrow string dtype

* TST: Fix shares_memory for arrow string dtype

* Fix more tests

* BUG: Index.getitem returning wrong result with negative step for arrow

* Update

* Update

* Fix

* Update array.py

* Fix

* Move

* Move

* Fix

* Add gh ref

* Update v2.1.4.rst

* Finish

* Update

* Update test_base.py

* Update test_old_base.py

* Update conftest.py

* Update conftest.py

* Update test_old_base.py

* Update

* Update test_setops.py

* Fix pre-commit
---
 pandas/conftest.py                            |  6 +-
 .../tests/indexes/base_class/test_formats.py  |  3 +
 .../tests/indexes/base_class/test_reshape.py  | 10 ++--
 .../tests/indexes/base_class/test_setops.py   |  2 +-
 .../tests/indexes/categorical/test_astype.py  |  2 +-
 .../indexes/categorical/test_category.py      |  5 +-
 .../tests/indexes/categorical/test_formats.py |  4 ++
 .../tests/indexes/categorical/test_reindex.py |  2 +-
 .../indexes/datetimes/methods/test_map.py     |  2 +-
 pandas/tests/indexes/interval/test_formats.py |  7 ++-
 .../tests/indexes/multi/test_constructors.py  |  7 ++-
 pandas/tests/indexes/multi/test_get_set.py    | 16 ++++--
 pandas/tests/indexes/multi/test_reindex.py    |  7 ++-
 pandas/tests/indexes/multi/test_setops.py     | 25 +++++---
 pandas/tests/indexes/object/test_astype.py    |  2 +-
 pandas/tests/indexes/object/test_indexing.py  | 51 ++++++++++++-----
 .../indexes/period/methods/test_astype.py     |  2 +-
 pandas/tests/indexes/test_base.py             | 57 +++++++++++++------
 pandas/tests/indexes/test_old_base.py         | 33 +++++++----
 pandas/tests/indexes/test_setops.py           |  4 +-
 .../indexes/timedeltas/methods/test_astype.py |  2 +-
 21 files changed, 173 insertions(+), 76 deletions(-)

diff --git a/pandas/conftest.py b/pandas/conftest.py
index 003474b57c8e1..7c829ed4b8cb9 100644
--- a/pandas/conftest.py
+++ b/pandas/conftest.py
@@ -1903,7 +1903,7 @@ def using_copy_on_write() -> bool:
 @pytest.fixture
 def warn_copy_on_write() -> bool:
     """
-    Fixture to check if Copy-on-Write is enabled.
+    Fixture to check if Copy-on-Write is in warning mode.
     """
     return (
         pd.options.mode.copy_on_write == "warn"
@@ -1914,9 +1914,9 @@ def warn_copy_on_write() -> bool:
 @pytest.fixture
 def using_infer_string() -> bool:
     """
-    Fixture to check if infer_string is enabled.
+    Fixture to check if infer string option is enabled.
     """
-    return pd.options.future.infer_string
+    return pd.options.future.infer_string is True
 
 
 warsaws = ["Europe/Warsaw", "dateutil/Europe/Warsaw"]
diff --git a/pandas/tests/indexes/base_class/test_formats.py b/pandas/tests/indexes/base_class/test_formats.py
index 379aea8826414..f30b578cfcf56 100644
--- a/pandas/tests/indexes/base_class/test_formats.py
+++ b/pandas/tests/indexes/base_class/test_formats.py
@@ -1,6 +1,7 @@
 import numpy as np
 import pytest
 
+from pandas._config import using_pyarrow_string_dtype
 import pandas._config.config as cf
 
 from pandas import Index
@@ -15,6 +16,7 @@ def test_repr_is_valid_construction_code(self):
         res = eval(repr(idx))
         tm.assert_index_equal(res, idx)
 
+    @pytest.mark.xfail(using_pyarrow_string_dtype(), reason="repr different")
     @pytest.mark.parametrize(
         "index,expected",
         [
@@ -79,6 +81,7 @@ def test_string_index_repr(self, index, expected):
         result = repr(index)
         assert result == expected
 
+    @pytest.mark.xfail(using_pyarrow_string_dtype(), reason="repr different")
     @pytest.mark.parametrize(
         "index,expected",
         [
diff --git a/pandas/tests/indexes/base_class/test_reshape.py b/pandas/tests/indexes/base_class/test_reshape.py
index 6586f5f9de480..814a6a516904b 100644
--- a/pandas/tests/indexes/base_class/test_reshape.py
+++ b/pandas/tests/indexes/base_class/test_reshape.py
@@ -33,13 +33,15 @@ def test_insert(self):
 
         # test empty
         null_index = Index([])
-        tm.assert_index_equal(Index(["a"]), null_index.insert(0, "a"))
+        tm.assert_index_equal(Index(["a"], dtype=object), null_index.insert(0, "a"))
 
-    def test_insert_missing(self, nulls_fixture):
+    def test_insert_missing(self, nulls_fixture, using_infer_string):
         # GH#22295
         # test there is no mangling of NA values
-        expected = Index(["a", nulls_fixture, "b", "c"])
-        result = Index(list("abc")).insert(1, nulls_fixture)
+        expected = Index(["a", nulls_fixture, "b", "c"], dtype=object)
+        result = Index(list("abc"), dtype=object).insert(
+            1, Index([nulls_fixture], dtype=object)
+        )
         tm.assert_index_equal(result, expected)
 
     @pytest.mark.parametrize(
diff --git a/pandas/tests/indexes/base_class/test_setops.py b/pandas/tests/indexes/base_class/test_setops.py
index e538ad512d691..3ef3f3ad4d3a2 100644
--- a/pandas/tests/indexes/base_class/test_setops.py
+++ b/pandas/tests/indexes/base_class/test_setops.py
@@ -154,7 +154,7 @@ def test_intersection_str_dates(self, sort):
     def test_intersection_non_monotonic_non_unique(self, index2, expected_arr, sort):
         # non-monotonic non-unique
         index1 = Index(["A", "B", "A", "C"])
-        expected = Index(expected_arr, dtype="object")
+        expected = Index(expected_arr)
         result = index1.intersection(index2, sort=sort)
         if sort is None:
             expected = expected.sort_values()
diff --git a/pandas/tests/indexes/categorical/test_astype.py b/pandas/tests/indexes/categorical/test_astype.py
index da1d692f9eb2d..a17627b7515b2 100644
--- a/pandas/tests/indexes/categorical/test_astype.py
+++ b/pandas/tests/indexes/categorical/test_astype.py
@@ -18,7 +18,7 @@ def test_astype(self):
         ci = CategoricalIndex(list("aabbca"), categories=list("cab"), ordered=False)
 
         result = ci.astype(object)
-        tm.assert_index_equal(result, Index(np.array(ci)))
+        tm.assert_index_equal(result, Index(np.array(ci), dtype=object))
 
         # this IS equal, but not the same class
         assert result.equals(ci)
diff --git a/pandas/tests/indexes/categorical/test_category.py b/pandas/tests/indexes/categorical/test_category.py
index 142a00d32815a..03a298a13dc2b 100644
--- a/pandas/tests/indexes/categorical/test_category.py
+++ b/pandas/tests/indexes/categorical/test_category.py
@@ -1,6 +1,8 @@
 import numpy as np
 import pytest
 
+from pandas._config import using_pyarrow_string_dtype
+
 from pandas._libs import index as libindex
 from pandas._libs.arrays import NDArrayBacked
 
@@ -47,7 +49,7 @@ def test_insert(self, simple_index):
 
         # invalid -> cast to object
         expected = ci.astype(object).insert(0, "d")
-        result = ci.insert(0, "d")
+        result = ci.insert(0, "d").astype(object)
         tm.assert_index_equal(result, expected, exact=True)
 
         # GH 18295 (test missing)
@@ -194,6 +196,7 @@ def test_unique(self, data, categories, expected_data, ordered):
         expected = CategoricalIndex(expected_data, dtype=dtype)
         tm.assert_index_equal(idx.unique(), expected)
 
+    @pytest.mark.xfail(using_pyarrow_string_dtype(), reason="repr doesn't roundtrip")
     def test_repr_roundtrip(self):
         ci = CategoricalIndex(["a", "b"], categories=["a", "b"], ordered=True)
         str(ci)
diff --git a/pandas/tests/indexes/categorical/test_formats.py b/pandas/tests/indexes/categorical/test_formats.py
index ea3e4ce213e67..522ca1bc2afde 100644
--- a/pandas/tests/indexes/categorical/test_formats.py
+++ b/pandas/tests/indexes/categorical/test_formats.py
@@ -1,6 +1,9 @@
 """
 Tests for CategoricalIndex.__repr__ and related methods.
 """
+import pytest
+
+from pandas._config import using_pyarrow_string_dtype
 import pandas._config.config as cf
 
 from pandas import CategoricalIndex
@@ -16,6 +19,7 @@ def test_format_different_scalar_lengths(self):
         with tm.assert_produces_warning(FutureWarning, match=msg):
             assert idx.format() == expected
 
+    @pytest.mark.xfail(using_pyarrow_string_dtype(), reason="repr different")
     def test_string_categorical_index_repr(self):
         # short
         idx = CategoricalIndex(["a", "bb", "ccc"])
diff --git a/pandas/tests/indexes/categorical/test_reindex.py b/pandas/tests/indexes/categorical/test_reindex.py
index 8ca5c6099b4e7..5b1f2b9fb159a 100644
--- a/pandas/tests/indexes/categorical/test_reindex.py
+++ b/pandas/tests/indexes/categorical/test_reindex.py
@@ -40,7 +40,7 @@ def test_reindex_duplicate_target(self):
         # See GH25459
         cat = CategoricalIndex(["a", "b", "c"], categories=["a", "b", "c", "d"])
         res, indexer = cat.reindex(["a", "c", "c"])
-        exp = Index(["a", "c", "c"], dtype="object")
+        exp = Index(["a", "c", "c"])
         tm.assert_index_equal(res, exp, exact=True)
         tm.assert_numpy_array_equal(indexer, np.array([0, 2, 2], dtype=np.intp))
 
diff --git a/pandas/tests/indexes/datetimes/methods/test_map.py b/pandas/tests/indexes/datetimes/methods/test_map.py
index c31e2407190ea..f35f07bd32068 100644
--- a/pandas/tests/indexes/datetimes/methods/test_map.py
+++ b/pandas/tests/indexes/datetimes/methods/test_map.py
@@ -16,7 +16,7 @@ def test_map(self):
 
         f = lambda x: x.strftime("%Y%m%d")
         result = rng.map(f)
-        exp = Index([f(x) for x in rng], dtype="<U8")
+        exp = Index([f(x) for x in rng])
         tm.assert_index_equal(result, exp)
 
     def test_map_fallthrough(self, capsys):
diff --git a/pandas/tests/indexes/interval/test_formats.py b/pandas/tests/indexes/interval/test_formats.py
index edd7993056512..3b8e18463160f 100644
--- a/pandas/tests/indexes/interval/test_formats.py
+++ b/pandas/tests/indexes/interval/test_formats.py
@@ -1,6 +1,8 @@
 import numpy as np
 import pytest
 
+from pandas._config import using_pyarrow_string_dtype
+
 from pandas import (
     DataFrame,
     DatetimeIndex,
@@ -31,13 +33,16 @@ class TestIntervalIndexRendering:
             (DataFrame, ("            0\n(0.0, 1.0]  a\nNaN         b\n(2.0, 3.0]  c")),
         ],
     )
-    def test_repr_missing(self, constructor, expected):
+    def test_repr_missing(self, constructor, expected, using_infer_string, request):
         # GH 25984
+        if using_infer_string and constructor is Series:
+            request.applymarker(pytest.mark.xfail(reason="repr different"))
         index = IntervalIndex.from_tuples([(0, 1), np.nan, (2, 3)])
         obj = constructor(list("abc"), index=index)
         result = repr(obj)
         assert result == expected
 
+    @pytest.mark.xfail(using_pyarrow_string_dtype(), reason="repr different")
     def test_repr_floats(self):
         # GH 32553
 
diff --git a/pandas/tests/indexes/multi/test_constructors.py b/pandas/tests/indexes/multi/test_constructors.py
index 32659bc2f7bff..8456e6a7acba5 100644
--- a/pandas/tests/indexes/multi/test_constructors.py
+++ b/pandas/tests/indexes/multi/test_constructors.py
@@ -847,11 +847,14 @@ def test_multiindex_inference_consistency():
     assert lev.dtype == object
 
 
-def test_dtype_representation():
+def test_dtype_representation(using_infer_string):
     # GH#46900
     pmidx = MultiIndex.from_arrays([[1], ["a"]], names=[("a", "b"), ("c", "d")])
     result = pmidx.dtypes
+    exp = "object" if not using_infer_string else "string"
     expected = Series(
-        ["int64", "object"], index=MultiIndex.from_tuples([("a", "b"), ("c", "d")])
+        ["int64", exp],
+        index=MultiIndex.from_tuples([("a", "b"), ("c", "d")]),
+        dtype=object,
     )
     tm.assert_series_equal(result, expected)
diff --git a/pandas/tests/indexes/multi/test_get_set.py b/pandas/tests/indexes/multi/test_get_set.py
index e362fc8a05a46..6eeaeb6711d03 100644
--- a/pandas/tests/indexes/multi/test_get_set.py
+++ b/pandas/tests/indexes/multi/test_get_set.py
@@ -34,23 +34,25 @@ def test_get_level_number_integer(idx):
         idx._get_level_number("fourth")
 
 
-def test_get_dtypes():
+def test_get_dtypes(using_infer_string):
     # Test MultiIndex.dtypes (# Gh37062)
     idx_multitype = MultiIndex.from_product(
         [[1, 2, 3], ["a", "b", "c"], pd.date_range("20200101", periods=2, tz="UTC")],
         names=["int", "string", "dt"],
     )
+
+    exp = "object" if not using_infer_string else "string"
     expected = pd.Series(
         {
             "int": np.dtype("int64"),
-            "string": np.dtype("O"),
+            "string": exp,
             "dt": DatetimeTZDtype(tz="utc"),
         }
     )
     tm.assert_series_equal(expected, idx_multitype.dtypes)
 
 
-def test_get_dtypes_no_level_name():
+def test_get_dtypes_no_level_name(using_infer_string):
     # Test MultiIndex.dtypes (# GH38580 )
     idx_multitype = MultiIndex.from_product(
         [
@@ -59,17 +61,18 @@ def test_get_dtypes_no_level_name():
             pd.date_range("20200101", periods=2, tz="UTC"),
         ],
     )
+    exp = "object" if not using_infer_string else "string"
     expected = pd.Series(
         {
             "level_0": np.dtype("int64"),
-            "level_1": np.dtype("O"),
+            "level_1": exp,
             "level_2": DatetimeTZDtype(tz="utc"),
         }
     )
     tm.assert_series_equal(expected, idx_multitype.dtypes)
 
 
-def test_get_dtypes_duplicate_level_names():
+def test_get_dtypes_duplicate_level_names(using_infer_string):
     # Test MultiIndex.dtypes with non-unique level names (# GH45174)
     result = MultiIndex.from_product(
         [
@@ -79,8 +82,9 @@ def test_get_dtypes_duplicate_level_names():
         ],
         names=["A", "A", "A"],
     ).dtypes
+    exp = "object" if not using_infer_string else "string"
     expected = pd.Series(
-        [np.dtype("int64"), np.dtype("O"), DatetimeTZDtype(tz="utc")],
+        [np.dtype("int64"), exp, DatetimeTZDtype(tz="utc")],
         index=["A", "A", "A"],
     )
     tm.assert_series_equal(result, expected)
diff --git a/pandas/tests/indexes/multi/test_reindex.py b/pandas/tests/indexes/multi/test_reindex.py
index 77a527134b79f..d1b4fe8b98760 100644
--- a/pandas/tests/indexes/multi/test_reindex.py
+++ b/pandas/tests/indexes/multi/test_reindex.py
@@ -75,11 +75,14 @@ def test_reindex_lvl_preserves_names_when_target_is_list_or_array():
     assert idx.reindex([], level=1)[0].names == ["foo", "bar"]
 
 
-def test_reindex_lvl_preserves_type_if_target_is_empty_list_or_array():
+def test_reindex_lvl_preserves_type_if_target_is_empty_list_or_array(
+    using_infer_string,
+):
     # GH7774
     idx = MultiIndex.from_product([[0, 1], ["a", "b"]])
     assert idx.reindex([], level=0)[0].levels[0].dtype.type == np.int64
-    assert idx.reindex([], level=1)[0].levels[1].dtype.type == np.object_
+    exp = np.object_ if not using_infer_string else str
+    assert idx.reindex([], level=1)[0].levels[1].dtype.type == exp
 
     # case with EA levels
     cat = pd.Categorical(["foo", "bar"])
diff --git a/pandas/tests/indexes/multi/test_setops.py b/pandas/tests/indexes/multi/test_setops.py
index be266f5d8fdce..0abb56ecf9de7 100644
--- a/pandas/tests/indexes/multi/test_setops.py
+++ b/pandas/tests/indexes/multi/test_setops.py
@@ -263,19 +263,23 @@ def test_union(idx, sort):
         assert result.equals(idx)
 
 
-def test_union_with_regular_index(idx):
+def test_union_with_regular_index(idx, using_infer_string):
     other = Index(["A", "B", "C"])
 
     result = other.union(idx)
     assert ("foo", "one") in result
     assert "B" in result
 
-    msg = "The values in the array are unorderable"
-    with tm.assert_produces_warning(RuntimeWarning, match=msg):
-        result2 = idx.union(other)
-    # This is more consistent now, if sorting fails then we don't sort at all
-    # in the MultiIndex case.
-    assert not result.equals(result2)
+    if using_infer_string:
+        with pytest.raises(NotImplementedError, match="Can only union"):
+            idx.union(other)
+    else:
+        msg = "The values in the array are unorderable"
+        with tm.assert_produces_warning(RuntimeWarning, match=msg):
+            result2 = idx.union(other)
+        # This is more consistent now, if sorting fails then we don't sort at all
+        # in the MultiIndex case.
+        assert not result.equals(result2)
 
 
 def test_intersection(idx, sort):
@@ -756,7 +760,12 @@ def test_intersection_keep_ea_dtypes(val, any_numeric_ea_dtype):
 
 def test_union_with_na_when_constructing_dataframe():
     # GH43222
-    series1 = Series((1,), index=MultiIndex.from_tuples(((None, None),)))
+    series1 = Series(
+        (1,),
+        index=MultiIndex.from_arrays(
+            [Series([None], dtype="string"), Series([None], dtype="string")]
+        ),
+    )
     series2 = Series((10, 20), index=MultiIndex.from_tuples(((None, None), ("a", "b"))))
     result = DataFrame([series1, series2])
     expected = DataFrame({(np.nan, np.nan): [1.0, 10.0], ("a", "b"): [np.nan, 20.0]})
diff --git a/pandas/tests/indexes/object/test_astype.py b/pandas/tests/indexes/object/test_astype.py
index 273b39b5e319d..9c1ef302c5b51 100644
--- a/pandas/tests/indexes/object/test_astype.py
+++ b/pandas/tests/indexes/object/test_astype.py
@@ -20,7 +20,7 @@ def test_astype_str_from_bytes():
 
     # while we're here, check that Series.astype behaves the same
     result = Series(idx).astype(str)
-    expected = Series(expected)
+    expected = Series(expected, dtype=object)
     tm.assert_series_equal(result, expected)
 
 
diff --git a/pandas/tests/indexes/object/test_indexing.py b/pandas/tests/indexes/object/test_indexing.py
index 93d46ebdd0b51..ebf9dac715f8d 100644
--- a/pandas/tests/indexes/object/test_indexing.py
+++ b/pandas/tests/indexes/object/test_indexing.py
@@ -3,7 +3,10 @@
 import numpy as np
 import pytest
 
-from pandas._libs.missing import is_matching_na
+from pandas._libs.missing import (
+    NA,
+    is_matching_na,
+)
 import pandas.util._test_decorators as td
 
 import pandas as pd
@@ -25,20 +28,36 @@ def test_get_indexer_strings(self, method, expected):
 
         tm.assert_numpy_array_equal(actual, expected)
 
-    def test_get_indexer_strings_raises(self):
+    def test_get_indexer_strings_raises(self, using_infer_string):
         index = Index(["b", "c"])
 
-        msg = r"unsupported operand type\(s\) for -: 'str' and 'str'"
-        with pytest.raises(TypeError, match=msg):
-            index.get_indexer(["a", "b", "c", "d"], method="nearest")
+        if using_infer_string:
+            import pyarrow as pa
 
-        with pytest.raises(TypeError, match=msg):
-            index.get_indexer(["a", "b", "c", "d"], method="pad", tolerance=2)
+            msg = "has no kernel"
+            with pytest.raises(pa.lib.ArrowNotImplementedError, match=msg):
+                index.get_indexer(["a", "b", "c", "d"], method="nearest")
 
-        with pytest.raises(TypeError, match=msg):
-            index.get_indexer(
-                ["a", "b", "c", "d"], method="pad", tolerance=[2, 2, 2, 2]
-            )
+            with pytest.raises(pa.lib.ArrowNotImplementedError, match=msg):
+                index.get_indexer(["a", "b", "c", "d"], method="pad", tolerance=2)
+
+            with pytest.raises(pa.lib.ArrowNotImplementedError, match=msg):
+                index.get_indexer(
+                    ["a", "b", "c", "d"], method="pad", tolerance=[2, 2, 2, 2]
+                )
+
+        else:
+            msg = r"unsupported operand type\(s\) for -: 'str' and 'str'"
+            with pytest.raises(TypeError, match=msg):
+                index.get_indexer(["a", "b", "c", "d"], method="nearest")
+
+            with pytest.raises(TypeError, match=msg):
+                index.get_indexer(["a", "b", "c", "d"], method="pad", tolerance=2)
+
+            with pytest.raises(TypeError, match=msg):
+                index.get_indexer(
+                    ["a", "b", "c", "d"], method="pad", tolerance=[2, 2, 2, 2]
+                )
 
     def test_get_indexer_with_NA_values(
         self, unique_nulls_fixture, unique_nulls_fixture2
@@ -51,15 +70,21 @@ def test_get_indexer_with_NA_values(
         arr = np.array([unique_nulls_fixture, unique_nulls_fixture2], dtype=object)
         index = Index(arr, dtype=object)
         result = index.get_indexer(
-            [unique_nulls_fixture, unique_nulls_fixture2, "Unknown"]
+            Index(
+                [unique_nulls_fixture, unique_nulls_fixture2, "Unknown"], dtype=object
+            )
         )
         expected = np.array([0, 1, -1], dtype=np.intp)
         tm.assert_numpy_array_equal(result, expected)
 
 
 class TestGetIndexerNonUnique:
-    def test_get_indexer_non_unique_nas(self, nulls_fixture):
+    def test_get_indexer_non_unique_nas(
+        self, nulls_fixture, request, using_infer_string
+    ):
         # even though this isn't non-unique, this should still work
+        if using_infer_string and (nulls_fixture is None or nulls_fixture is NA):
+            request.applymarker(pytest.mark.xfail(reason="NAs are cast to NaN"))
         index = Index(["a", "b", nulls_fixture])
         indexer, missing = index.get_indexer_non_unique([nulls_fixture])
 
diff --git a/pandas/tests/indexes/period/methods/test_astype.py b/pandas/tests/indexes/period/methods/test_astype.py
index ba60ffd1fff4d..d545bfd2fae0f 100644
--- a/pandas/tests/indexes/period/methods/test_astype.py
+++ b/pandas/tests/indexes/period/methods/test_astype.py
@@ -41,7 +41,7 @@ def test_astype_conversion(self):
         tm.assert_index_equal(result, expected)
 
         result = idx.astype(str)
-        expected = Index([str(x) for x in idx], name="idx")
+        expected = Index([str(x) for x in idx], name="idx", dtype=object)
         tm.assert_index_equal(result, expected)
 
         idx = period_range("1990", "2009", freq="Y", name="idx")
diff --git a/pandas/tests/indexes/test_base.py b/pandas/tests/indexes/test_base.py
index 2b0bb884f0706..185e34efdc177 100644
--- a/pandas/tests/indexes/test_base.py
+++ b/pandas/tests/indexes/test_base.py
@@ -72,12 +72,17 @@ def test_constructor_casting(self, index):
         tm.assert_index_equal(index, new_index)
 
     @pytest.mark.parametrize("index", ["string"], indirect=True)
-    def test_constructor_copy(self, index):
+    def test_constructor_copy(self, index, using_infer_string):
         arr = np.array(index)
         new_index = Index(arr, copy=True, name="name")
         assert isinstance(new_index, Index)
         assert new_index.name == "name"
-        tm.assert_numpy_array_equal(arr, new_index.values)
+        if using_infer_string:
+            tm.assert_extension_array_equal(
+                new_index.values, pd.array(arr, dtype="string[pyarrow_numpy]")
+            )
+        else:
+            tm.assert_numpy_array_equal(arr, new_index.values)
         arr[0] = "SOMEBIGLONGSTRING"
         assert new_index[0] != "SOMEBIGLONGSTRING"
 
@@ -145,7 +150,7 @@ def test_constructor_from_series_freq(self):
 
         tm.assert_index_equal(result, expected)
 
-    def test_constructor_from_frame_series_freq(self):
+    def test_constructor_from_frame_series_freq(self, using_infer_string):
         # GH 6273
         # create from a series, passing a freq
         dts = ["1-1-1990", "2-1-1990", "3-1-1990", "4-1-1990", "5-1-1990"]
@@ -154,8 +159,8 @@ def test_constructor_from_frame_series_freq(self):
         df = DataFrame(np.random.default_rng(2).random((5, 3)))
         df["date"] = dts
         result = DatetimeIndex(df["date"], freq="MS")
-
-        assert df["date"].dtype == object
+        dtype = object if not using_infer_string else "string"
+        assert df["date"].dtype == dtype
         expected.name = "date"
         tm.assert_index_equal(result, expected)
 
@@ -164,8 +169,10 @@ def test_constructor_from_frame_series_freq(self):
 
         # GH 6274
         # infer freq of same
-        freq = pd.infer_freq(df["date"])
-        assert freq == "MS"
+        if not using_infer_string:
+            # Doesn't work with arrow strings
+            freq = pd.infer_freq(df["date"])
+            assert freq == "MS"
 
     def test_constructor_int_dtype_nan(self):
         # see gh-15187
@@ -346,6 +353,9 @@ def test_view_with_args_object_array_raises(self, index):
             msg = "When changing to a larger dtype"
             with pytest.raises(ValueError, match=msg):
                 index.view("i8")
+        elif index.dtype == "string":
+            with pytest.raises(NotImplementedError, match="i8"):
+                index.view("i8")
         else:
             msg = "Cannot change data-type for object array"
             with pytest.raises(TypeError, match=msg):
@@ -459,7 +469,9 @@ def test_fancy(self, simple_index):
         indirect=True,
     )
     @pytest.mark.parametrize("dtype", [int, np.bool_])
-    def test_empty_fancy(self, index, dtype):
+    def test_empty_fancy(self, index, dtype, request, using_infer_string):
+        if dtype is np.bool_ and using_infer_string and index.dtype == "string":
+            request.applymarker(pytest.mark.xfail(reason="numpy behavior is buggy"))
         empty_arr = np.array([], dtype=dtype)
         empty_index = type(index)([], dtype=index.dtype)
 
@@ -483,7 +495,7 @@ def test_empty_fancy_raises(self, index):
 
         assert index[[]].identical(empty_index)
         # np.ndarray only accepts ndarray of int & bool dtypes, so should Index
-        msg = r"arrays used as indices must be of integer \(or boolean\) type"
+        msg = r"arrays used as indices must be of integer"
         with pytest.raises(IndexError, match=msg):
             index[empty_farr]
 
@@ -665,7 +677,9 @@ def test_is_numeric(self, index, expected):
         ],
         indirect=["index"],
     )
-    def test_is_object(self, index, expected):
+    def test_is_object(self, index, expected, using_infer_string):
+        if using_infer_string and index.dtype == "string" and expected:
+            expected = False
         assert is_object_dtype(index) is expected
 
     def test_summary(self, index):
@@ -785,7 +799,7 @@ def test_drop_by_numeric_label_errors_ignore(self, key, expected):
     def test_drop_tuple(self, values, to_drop):
         # GH 18304
         index = Index(values)
-        expected = Index(["b"])
+        expected = Index(["b"], dtype=object)
 
         result = index.drop(to_drop)
         tm.assert_index_equal(result, expected)
@@ -838,9 +852,12 @@ def test_isin(self, values, index, expected):
         result = index.isin(values)
         tm.assert_numpy_array_equal(result, expected)
 
-    def test_isin_nan_common_object(self, nulls_fixture, nulls_fixture2):
+    def test_isin_nan_common_object(
+        self, nulls_fixture, nulls_fixture2, using_infer_string
+    ):
         # Test cartesian product of null fixtures and ensure that we don't
         # mangle the various types (save a corner case with PyPy)
+        idx = Index(["a", nulls_fixture])
 
         # all nans are the same
         if (
@@ -850,19 +867,25 @@ def test_isin_nan_common_object(self, nulls_fixture, nulls_fixture2):
             and math.isnan(nulls_fixture2)
         ):
             tm.assert_numpy_array_equal(
-                Index(["a", nulls_fixture]).isin([nulls_fixture2]),
+                idx.isin([nulls_fixture2]),
                 np.array([False, True]),
             )
 
         elif nulls_fixture is nulls_fixture2:  # should preserve NA type
             tm.assert_numpy_array_equal(
-                Index(["a", nulls_fixture]).isin([nulls_fixture2]),
+                idx.isin([nulls_fixture2]),
+                np.array([False, True]),
+            )
+
+        elif using_infer_string and idx.dtype == "string":
+            tm.assert_numpy_array_equal(
+                idx.isin([nulls_fixture2]),
                 np.array([False, True]),
             )
 
         else:
             tm.assert_numpy_array_equal(
-                Index(["a", nulls_fixture]).isin([nulls_fixture2]),
+                idx.isin([nulls_fixture2]),
                 np.array([False, False]),
             )
 
@@ -1139,7 +1162,7 @@ def test_reindex_preserves_name_if_target_is_list_or_ndarray(self, name, labels)
     def test_reindex_preserves_type_if_target_is_empty_list_or_array(self, labels):
         # GH7774
         index = Index(list("abc"))
-        assert index.reindex(labels)[0].dtype.type == np.object_
+        assert index.reindex(labels)[0].dtype.type == index.dtype.type
 
     @pytest.mark.parametrize(
         "labels,dtype",
@@ -1231,7 +1254,7 @@ def test_equals_op_mismatched_multiindex_raises(self, index):
         with pytest.raises(ValueError, match="Lengths must match"):
             df.index == index
 
-    def test_equals_op_index_vs_mi_same_length(self):
+    def test_equals_op_index_vs_mi_same_length(self, using_infer_string):
         mi = MultiIndex.from_tuples([(1, 2), (4, 5), (8, 9)])
         index = Index(["foo", "bar", "baz"])
 
diff --git a/pandas/tests/indexes/test_old_base.py b/pandas/tests/indexes/test_old_base.py
index fd0d984053bd6..1787379b0faee 100644
--- a/pandas/tests/indexes/test_old_base.py
+++ b/pandas/tests/indexes/test_old_base.py
@@ -6,6 +6,8 @@
 import numpy as np
 import pytest
 
+from pandas._config import using_pyarrow_string_dtype
+
 from pandas._libs.tslibs import Timestamp
 
 from pandas.core.dtypes.common import (
@@ -210,7 +212,7 @@ def test_numeric_compat(self, simple_index):
             1 // idx
 
     def test_logical_compat(self, simple_index):
-        if simple_index.dtype == object:
+        if simple_index.dtype in (object, "string"):
             pytest.skip("Tested elsewhere.")
         idx = simple_index
         if idx.dtype.kind in "iufcbm":
@@ -298,7 +300,7 @@ def test_ensure_copied_data(self, index):
                 tm.assert_numpy_array_equal(
                     index._values._ndarray, result._values._ndarray, check_same="same"
                 )
-            elif index.dtype == "string[pyarrow]":
+            elif index.dtype in ("string[pyarrow]", "string[pyarrow_numpy]"):
                 assert tm.shares_memory(result._values, index._values)
             else:
                 raise NotImplementedError(index.dtype)
@@ -423,6 +425,10 @@ def test_insert_base(self, index):
             result = trimmed.insert(0, index[0])
         assert index[0:4].equals(result)
 
+    @pytest.mark.skipif(
+        using_pyarrow_string_dtype(),
+        reason="completely different behavior, tested elsewher",
+    )
     def test_insert_out_of_bounds(self, index):
         # TypeError/IndexError matches what np.insert raises in these cases
 
@@ -703,7 +709,7 @@ def test_map_str(self, simple_index):
             pytest.skip("See test_map.py")
         idx = simple_index
         result = idx.map(str)
-        expected = Index([str(x) for x in idx], dtype=object)
+        expected = Index([str(x) for x in idx])
         tm.assert_index_equal(result, expected)
 
     @pytest.mark.parametrize("copy", [True, False])
@@ -768,15 +774,15 @@ def test_getitem_2d_deprecated(self, simple_index):
         if isinstance(simple_index, IntervalIndex):
             pytest.skip("Tested elsewhere")
         idx = simple_index
-        msg = "Multi-dimensional indexing"
-        with pytest.raises(ValueError, match=msg):
+        msg = "Multi-dimensional indexing|too many|only"
+        with pytest.raises((ValueError, IndexError), match=msg):
             idx[:, None]
 
         if not isinstance(idx, RangeIndex):
             # GH#44051 RangeIndex already raised pre-2.0 with a different message
-            with pytest.raises(ValueError, match=msg):
+            with pytest.raises((ValueError, IndexError), match=msg):
                 idx[True]
-            with pytest.raises(ValueError, match=msg):
+            with pytest.raises((ValueError, IndexError), match=msg):
                 idx[False]
         else:
             msg = "only integers, slices"
@@ -840,7 +846,7 @@ def test_append_preserves_dtype(self, simple_index):
         alt = index.take(list(range(N)) * 2)
         tm.assert_index_equal(result, alt, check_exact=True)
 
-    def test_inv(self, simple_index):
+    def test_inv(self, simple_index, using_infer_string):
         idx = simple_index
 
         if idx.dtype.kind in ["i", "u"]:
@@ -853,14 +859,21 @@ def test_inv(self, simple_index):
             tm.assert_series_equal(res2, Series(expected))
         else:
             if idx.dtype.kind == "f":
+                err = TypeError
                 msg = "ufunc 'invert' not supported for the input types"
+            elif using_infer_string and idx.dtype == "string":
+                import pyarrow as pa
+
+                err = pa.lib.ArrowNotImplementedError
+                msg = "has no kernel"
             else:
+                err = TypeError
                 msg = "bad operand"
-            with pytest.raises(TypeError, match=msg):
+            with pytest.raises(err, match=msg):
                 ~idx
 
             # check that we get the same behavior with Series
-            with pytest.raises(TypeError, match=msg):
+            with pytest.raises(err, match=msg):
                 ~Series(idx)
 
     def test_is_boolean_is_deprecated(self, simple_index):
diff --git a/pandas/tests/indexes/test_setops.py b/pandas/tests/indexes/test_setops.py
index a489c51a808fd..4a6982cf98670 100644
--- a/pandas/tests/indexes/test_setops.py
+++ b/pandas/tests/indexes/test_setops.py
@@ -802,10 +802,10 @@ def test_union_identity(self, index, sort):
 
         # This should no longer be the same object, since [] is not consistent,
         # both objects will be recast to dtype('O')
-        union = first.union([], sort=sort)
+        union = first.union(Index([], dtype=first.dtype), sort=sort)
         assert (union is first) is (not sort)
 
-        union = Index([]).union(first, sort=sort)
+        union = Index([], dtype=first.dtype).union(first, sort=sort)
         assert (union is first) is (not sort)
 
     @pytest.mark.parametrize("index", ["string"], indirect=True)
diff --git a/pandas/tests/indexes/timedeltas/methods/test_astype.py b/pandas/tests/indexes/timedeltas/methods/test_astype.py
index 6aeb1fc23dae9..311f2b5c9aa59 100644
--- a/pandas/tests/indexes/timedeltas/methods/test_astype.py
+++ b/pandas/tests/indexes/timedeltas/methods/test_astype.py
@@ -61,7 +61,7 @@ def test_astype(self):
         tm.assert_index_equal(result, expected)
 
         result = idx.astype(str)
-        expected = Index([str(x) for x in idx], name="idx")
+        expected = Index([str(x) for x in idx], name="idx", dtype=object)
         tm.assert_index_equal(result, expected)
 
         rng = timedelta_range("1 days", periods=10)

From a61c556f6abdac6284bc27c52eb2ee452c543495 Mon Sep 17 00:00:00 2001
From: Patrick Hoefler <61934744+phofl@users.noreply.github.com>
Date: Sat, 9 Dec 2023 20:24:30 +0100
Subject: [PATCH 14/15] Adjust tests in strings folder for new string option
 (#56159)

* Adjust tests in strings folder for new string option

* BUG: translate losing object dtype with new string dtype

* Fix

* BUG: Index.str.cat casting result always to object

* Update accessor.py

* Fix further bugs

* Fix

* Fix tests

* Update accessor.py
---
 pandas/core/strings/accessor.py              | 33 ++++++++++++++----
 pandas/tests/strings/test_api.py             |  4 ++-
 pandas/tests/strings/test_case_justify.py    | 35 ++++++++++++++------
 pandas/tests/strings/test_extract.py         | 15 ++++++---
 pandas/tests/strings/test_find_replace.py    | 24 ++++++++------
 pandas/tests/strings/test_split_partition.py |  8 +++--
 pandas/tests/strings/test_string_array.py    |  4 ++-
 pandas/tests/strings/test_strings.py         | 20 ++++++-----
 8 files changed, 97 insertions(+), 46 deletions(-)

diff --git a/pandas/core/strings/accessor.py b/pandas/core/strings/accessor.py
index 127aee24e094f..75866c6f6013a 100644
--- a/pandas/core/strings/accessor.py
+++ b/pandas/core/strings/accessor.py
@@ -918,7 +918,13 @@ def split(
         if is_re(pat):
             regex = True
         result = self._data.array._str_split(pat, n, expand, regex)
-        return self._wrap_result(result, returns_string=expand, expand=expand)
+        if self._data.dtype == "category":
+            dtype = self._data.dtype.categories.dtype
+        else:
+            dtype = object if self._data.dtype == object else None
+        return self._wrap_result(
+            result, expand=expand, returns_string=expand, dtype=dtype
+        )
 
     @Appender(
         _shared_docs["str_split"]
@@ -936,7 +942,10 @@ def split(
     @forbid_nonstring_types(["bytes"])
     def rsplit(self, pat=None, *, n=-1, expand: bool = False):
         result = self._data.array._str_rsplit(pat, n=n)
-        return self._wrap_result(result, expand=expand, returns_string=expand)
+        dtype = object if self._data.dtype == object else None
+        return self._wrap_result(
+            result, expand=expand, returns_string=expand, dtype=dtype
+        )
 
     _shared_docs[
         "str_partition"
@@ -1032,7 +1041,13 @@ def rsplit(self, pat=None, *, n=-1, expand: bool = False):
     @forbid_nonstring_types(["bytes"])
     def partition(self, sep: str = " ", expand: bool = True):
         result = self._data.array._str_partition(sep, expand)
-        return self._wrap_result(result, expand=expand, returns_string=expand)
+        if self._data.dtype == "category":
+            dtype = self._data.dtype.categories.dtype
+        else:
+            dtype = object if self._data.dtype == object else None
+        return self._wrap_result(
+            result, expand=expand, returns_string=expand, dtype=dtype
+        )
 
     @Appender(
         _shared_docs["str_partition"]
@@ -1046,7 +1061,13 @@ def partition(self, sep: str = " ", expand: bool = True):
     @forbid_nonstring_types(["bytes"])
     def rpartition(self, sep: str = " ", expand: bool = True):
         result = self._data.array._str_rpartition(sep, expand)
-        return self._wrap_result(result, expand=expand, returns_string=expand)
+        if self._data.dtype == "category":
+            dtype = self._data.dtype.categories.dtype
+        else:
+            dtype = object if self._data.dtype == object else None
+        return self._wrap_result(
+            result, expand=expand, returns_string=expand, dtype=dtype
+        )
 
     def get(self, i):
         """
@@ -2752,7 +2773,7 @@ def extract(
         else:
             name = _get_single_group_name(regex)
             result = self._data.array._str_extract(pat, flags=flags, expand=returns_df)
-        return self._wrap_result(result, name=name)
+        return self._wrap_result(result, name=name, dtype=result_dtype)
 
     @forbid_nonstring_types(["bytes"])
     def extractall(self, pat, flags: int = 0) -> DataFrame:
@@ -3492,7 +3513,7 @@ def str_extractall(arr, pat, flags: int = 0) -> DataFrame:
         raise ValueError("pattern contains no capture groups")
 
     if isinstance(arr, ABCIndex):
-        arr = arr.to_series().reset_index(drop=True)
+        arr = arr.to_series().reset_index(drop=True).astype(arr.dtype)
 
     columns = _get_group_names(regex)
     match_list = []
diff --git a/pandas/tests/strings/test_api.py b/pandas/tests/strings/test_api.py
index fd2501835318d..31e005466af7b 100644
--- a/pandas/tests/strings/test_api.py
+++ b/pandas/tests/strings/test_api.py
@@ -8,6 +8,7 @@
     MultiIndex,
     Series,
     _testing as tm,
+    option_context,
 )
 from pandas.core.strings.accessor import StringMethods
 
@@ -163,7 +164,8 @@ def test_api_per_method(
 
     if inferred_dtype in allowed_types:
         # xref GH 23555, GH 23556
-        method(*args, **kwargs)  # works!
+        with option_context("future.no_silent_downcasting", True):
+            method(*args, **kwargs)  # works!
     else:
         # GH 23011, GH 23163
         msg = (
diff --git a/pandas/tests/strings/test_case_justify.py b/pandas/tests/strings/test_case_justify.py
index 1dee25e631648..41aedae90ca76 100644
--- a/pandas/tests/strings/test_case_justify.py
+++ b/pandas/tests/strings/test_case_justify.py
@@ -21,7 +21,8 @@ def test_title_mixed_object():
     s = Series(["FOO", np.nan, "bar", True, datetime.today(), "blah", None, 1, 2.0])
     result = s.str.title()
     expected = Series(
-        ["Foo", np.nan, "Bar", np.nan, np.nan, "Blah", None, np.nan, np.nan]
+        ["Foo", np.nan, "Bar", np.nan, np.nan, "Blah", None, np.nan, np.nan],
+        dtype=object,
     )
     tm.assert_almost_equal(result, expected)
 
@@ -41,11 +42,15 @@ def test_lower_upper_mixed_object():
     s = Series(["a", np.nan, "b", True, datetime.today(), "foo", None, 1, 2.0])
 
     result = s.str.upper()
-    expected = Series(["A", np.nan, "B", np.nan, np.nan, "FOO", None, np.nan, np.nan])
+    expected = Series(
+        ["A", np.nan, "B", np.nan, np.nan, "FOO", None, np.nan, np.nan], dtype=object
+    )
     tm.assert_series_equal(result, expected)
 
     result = s.str.lower()
-    expected = Series(["a", np.nan, "b", np.nan, np.nan, "foo", None, np.nan, np.nan])
+    expected = Series(
+        ["a", np.nan, "b", np.nan, np.nan, "foo", None, np.nan, np.nan], dtype=object
+    )
     tm.assert_series_equal(result, expected)
 
 
@@ -71,7 +76,8 @@ def test_capitalize_mixed_object():
     s = Series(["FOO", np.nan, "bar", True, datetime.today(), "blah", None, 1, 2.0])
     result = s.str.capitalize()
     expected = Series(
-        ["Foo", np.nan, "Bar", np.nan, np.nan, "Blah", None, np.nan, np.nan]
+        ["Foo", np.nan, "Bar", np.nan, np.nan, "Blah", None, np.nan, np.nan],
+        dtype=object,
     )
     tm.assert_series_equal(result, expected)
 
@@ -87,7 +93,8 @@ def test_swapcase_mixed_object():
     s = Series(["FOO", np.nan, "bar", True, datetime.today(), "Blah", None, 1, 2.0])
     result = s.str.swapcase()
     expected = Series(
-        ["foo", np.nan, "BAR", np.nan, np.nan, "bLAH", None, np.nan, np.nan]
+        ["foo", np.nan, "BAR", np.nan, np.nan, "bLAH", None, np.nan, np.nan],
+        dtype=object,
     )
     tm.assert_series_equal(result, expected)
 
@@ -138,19 +145,22 @@ def test_pad_mixed_object():
 
     result = s.str.pad(5, side="left")
     expected = Series(
-        ["    a", np.nan, "    b", np.nan, np.nan, "   ee", None, np.nan, np.nan]
+        ["    a", np.nan, "    b", np.nan, np.nan, "   ee", None, np.nan, np.nan],
+        dtype=object,
     )
     tm.assert_series_equal(result, expected)
 
     result = s.str.pad(5, side="right")
     expected = Series(
-        ["a    ", np.nan, "b    ", np.nan, np.nan, "ee   ", None, np.nan, np.nan]
+        ["a    ", np.nan, "b    ", np.nan, np.nan, "ee   ", None, np.nan, np.nan],
+        dtype=object,
     )
     tm.assert_series_equal(result, expected)
 
     result = s.str.pad(5, side="both")
     expected = Series(
-        ["  a  ", np.nan, "  b  ", np.nan, np.nan, "  ee ", None, np.nan, np.nan]
+        ["  a  ", np.nan, "  b  ", np.nan, np.nan, "  ee ", None, np.nan, np.nan],
+        dtype=object,
     )
     tm.assert_series_equal(result, expected)
 
@@ -238,7 +248,8 @@ def test_center_ljust_rjust_mixed_object():
             None,
             np.nan,
             np.nan,
-        ]
+        ],
+        dtype=object,
     )
     tm.assert_series_equal(result, expected)
 
@@ -255,7 +266,8 @@ def test_center_ljust_rjust_mixed_object():
             None,
             np.nan,
             np.nan,
-        ]
+        ],
+        dtype=object,
     )
     tm.assert_series_equal(result, expected)
 
@@ -272,7 +284,8 @@ def test_center_ljust_rjust_mixed_object():
             None,
             np.nan,
             np.nan,
-        ]
+        ],
+        dtype=object,
     )
     tm.assert_series_equal(result, expected)
 
diff --git a/pandas/tests/strings/test_extract.py b/pandas/tests/strings/test_extract.py
index 9ad9b1eca41d9..77d008c650264 100644
--- a/pandas/tests/strings/test_extract.py
+++ b/pandas/tests/strings/test_extract.py
@@ -47,13 +47,16 @@ def test_extract_expand_False_mixed_object():
     # two groups
     result = ser.str.extract(".*(BAD[_]+).*(BAD)", expand=False)
     er = [np.nan, np.nan]  # empty row
-    expected = DataFrame([["BAD_", "BAD"], er, ["BAD_", "BAD"], er, er, er, er, er, er])
+    expected = DataFrame(
+        [["BAD_", "BAD"], er, ["BAD_", "BAD"], er, er, er, er, er, er], dtype=object
+    )
     tm.assert_frame_equal(result, expected)
 
     # single group
     result = ser.str.extract(".*(BAD[_]+).*BAD", expand=False)
     expected = Series(
-        ["BAD_", np.nan, "BAD_", np.nan, np.nan, np.nan, None, np.nan, np.nan]
+        ["BAD_", np.nan, "BAD_", np.nan, np.nan, np.nan, None, np.nan, np.nan],
+        dtype=object,
     )
     tm.assert_series_equal(result, expected)
 
@@ -238,7 +241,9 @@ def test_extract_expand_True_mixed_object():
     )
 
     result = mixed.str.extract(".*(BAD[_]+).*(BAD)", expand=True)
-    expected = DataFrame([["BAD_", "BAD"], er, ["BAD_", "BAD"], er, er, er, er, er, er])
+    expected = DataFrame(
+        [["BAD_", "BAD"], er, ["BAD_", "BAD"], er, er, er, er, er, er], dtype=object
+    )
     tm.assert_frame_equal(result, expected)
 
 
@@ -603,8 +608,8 @@ def test_extractall_stringindex(any_string_dtype):
     # index.name doesn't affect to the result
     if any_string_dtype == "object":
         for idx in [
-            Index(["a1a2", "b1", "c1"]),
-            Index(["a1a2", "b1", "c1"], name="xxx"),
+            Index(["a1a2", "b1", "c1"], dtype=object),
+            Index(["a1a2", "b1", "c1"], name="xxx", dtype=object),
         ]:
             result = idx.str.extractall(r"[ab](?P<digit>\d)")
             tm.assert_frame_equal(result, expected)
diff --git a/pandas/tests/strings/test_find_replace.py b/pandas/tests/strings/test_find_replace.py
index bd64a5dce3b9a..3f58c6d703f8f 100644
--- a/pandas/tests/strings/test_find_replace.py
+++ b/pandas/tests/strings/test_find_replace.py
@@ -242,7 +242,7 @@ def test_contains_nan(any_string_dtype):
 
 
 @pytest.mark.parametrize("pat", ["foo", ("foo", "baz")])
-@pytest.mark.parametrize("dtype", [None, "category"])
+@pytest.mark.parametrize("dtype", ["object", "category"])
 @pytest.mark.parametrize("null_value", [None, np.nan, pd.NA])
 @pytest.mark.parametrize("na", [True, False])
 def test_startswith(pat, dtype, null_value, na):
@@ -254,10 +254,10 @@ def test_startswith(pat, dtype, null_value, na):
 
     result = values.str.startswith(pat)
     exp = Series([False, np.nan, True, False, False, np.nan, True])
-    if dtype is None and null_value is pd.NA:
+    if dtype == "object" and null_value is pd.NA:
         # GH#18463
         exp = exp.fillna(null_value)
-    elif dtype is None and null_value is None:
+    elif dtype == "object" and null_value is None:
         exp[exp.isna()] = None
     tm.assert_series_equal(result, exp)
 
@@ -300,7 +300,7 @@ def test_startswith_nullable_string_dtype(nullable_string_dtype, na):
 
 
 @pytest.mark.parametrize("pat", ["foo", ("foo", "baz")])
-@pytest.mark.parametrize("dtype", [None, "category"])
+@pytest.mark.parametrize("dtype", ["object", "category"])
 @pytest.mark.parametrize("null_value", [None, np.nan, pd.NA])
 @pytest.mark.parametrize("na", [True, False])
 def test_endswith(pat, dtype, null_value, na):
@@ -312,10 +312,10 @@ def test_endswith(pat, dtype, null_value, na):
 
     result = values.str.endswith(pat)
     exp = Series([False, np.nan, False, False, True, np.nan, True])
-    if dtype is None and null_value is pd.NA:
+    if dtype == "object" and null_value is pd.NA:
         # GH#18463
-        exp = exp.fillna(pd.NA)
-    elif dtype is None and null_value is None:
+        exp = exp.fillna(null_value)
+    elif dtype == "object" and null_value is None:
         exp[exp.isna()] = None
     tm.assert_series_equal(result, exp)
 
@@ -382,7 +382,9 @@ def test_replace_mixed_object():
         ["aBAD", np.nan, "bBAD", True, datetime.today(), "fooBAD", None, 1, 2.0]
     )
     result = Series(ser).str.replace("BAD[_]*", "", regex=True)
-    expected = Series(["a", np.nan, "b", np.nan, np.nan, "foo", None, np.nan, np.nan])
+    expected = Series(
+        ["a", np.nan, "b", np.nan, np.nan, "foo", None, np.nan, np.nan], dtype=object
+    )
     tm.assert_series_equal(result, expected)
 
 
@@ -469,7 +471,9 @@ def test_replace_compiled_regex_mixed_object():
         ["aBAD", np.nan, "bBAD", True, datetime.today(), "fooBAD", None, 1, 2.0]
     )
     result = Series(ser).str.replace(pat, "", regex=True)
-    expected = Series(["a", np.nan, "b", np.nan, np.nan, "foo", None, np.nan, np.nan])
+    expected = Series(
+        ["a", np.nan, "b", np.nan, np.nan, "foo", None, np.nan, np.nan], dtype=object
+    )
     tm.assert_series_equal(result, expected)
 
 
@@ -913,7 +917,7 @@ def test_translate_mixed_object():
     # Series with non-string values
     s = Series(["a", "b", "c", 1.2])
     table = str.maketrans("abc", "cde")
-    expected = Series(["c", "d", "e", np.nan])
+    expected = Series(["c", "d", "e", np.nan], dtype=object)
     result = s.str.translate(table)
     tm.assert_series_equal(result, expected)
 
diff --git a/pandas/tests/strings/test_split_partition.py b/pandas/tests/strings/test_split_partition.py
index 0a7d409773dd6..9ff1fc0e13ae9 100644
--- a/pandas/tests/strings/test_split_partition.py
+++ b/pandas/tests/strings/test_split_partition.py
@@ -681,14 +681,16 @@ def test_partition_sep_kwarg(any_string_dtype, method):
 def test_get():
     ser = Series(["a_b_c", "c_d_e", np.nan, "f_g_h"])
     result = ser.str.split("_").str.get(1)
-    expected = Series(["b", "d", np.nan, "g"])
+    expected = Series(["b", "d", np.nan, "g"], dtype=object)
     tm.assert_series_equal(result, expected)
 
 
 def test_get_mixed_object():
     ser = Series(["a_b_c", np.nan, "c_d_e", True, datetime.today(), None, 1, 2.0])
     result = ser.str.split("_").str.get(1)
-    expected = Series(["b", np.nan, "d", np.nan, np.nan, None, np.nan, np.nan])
+    expected = Series(
+        ["b", np.nan, "d", np.nan, np.nan, None, np.nan, np.nan], dtype=object
+    )
     tm.assert_series_equal(result, expected)
 
 
@@ -696,7 +698,7 @@ def test_get_mixed_object():
 def test_get_bounds(idx):
     ser = Series(["1_2_3_4_5", "6_7_8_9_10", "11_12"])
     result = ser.str.split("_").str.get(idx)
-    expected = Series(["3", "8", np.nan])
+    expected = Series(["3", "8", np.nan], dtype=object)
     tm.assert_series_equal(result, expected)
 
 
diff --git a/pandas/tests/strings/test_string_array.py b/pandas/tests/strings/test_string_array.py
index a88dcc8956931..0b3f368afea5e 100644
--- a/pandas/tests/strings/test_string_array.py
+++ b/pandas/tests/strings/test_string_array.py
@@ -8,6 +8,7 @@
     DataFrame,
     Series,
     _testing as tm,
+    option_context,
 )
 
 
@@ -56,7 +57,8 @@ def test_string_array(nullable_string_dtype, any_string_method):
         columns = expected.select_dtypes(include="object").columns
         assert all(result[columns].dtypes == nullable_string_dtype)
         result[columns] = result[columns].astype(object)
-        expected[columns] = expected[columns].fillna(NA)  # GH#18463
+        with option_context("future.no_silent_downcasting", True):
+            expected[columns] = expected[columns].fillna(NA)  # GH#18463
 
     tm.assert_equal(result, expected)
 
diff --git a/pandas/tests/strings/test_strings.py b/pandas/tests/strings/test_strings.py
index 4315835b70a40..f662dfd7e2b14 100644
--- a/pandas/tests/strings/test_strings.py
+++ b/pandas/tests/strings/test_strings.py
@@ -76,7 +76,8 @@ def test_repeat_mixed_object():
     ser = Series(["a", np.nan, "b", True, datetime.today(), "foo", None, 1, 2.0])
     result = ser.str.repeat(3)
     expected = Series(
-        ["aaa", np.nan, "bbb", np.nan, np.nan, "foofoofoo", None, np.nan, np.nan]
+        ["aaa", np.nan, "bbb", np.nan, np.nan, "foofoofoo", None, np.nan, np.nan],
+        dtype=object,
     )
     tm.assert_series_equal(result, expected)
 
@@ -270,7 +271,8 @@ def test_spilt_join_roundtrip_mixed_object():
     )
     result = ser.str.split("_").str.join("_")
     expected = Series(
-        ["a_b", np.nan, "asdf_cas_asdf", np.nan, np.nan, "foo", None, np.nan, np.nan]
+        ["a_b", np.nan, "asdf_cas_asdf", np.nan, np.nan, "foo", None, np.nan, np.nan],
+        dtype=object,
     )
     tm.assert_series_equal(result, expected)
 
@@ -398,7 +400,7 @@ def test_slice(start, stop, step, expected, any_string_dtype):
 def test_slice_mixed_object(start, stop, step, expected):
     ser = Series(["aafootwo", np.nan, "aabartwo", True, datetime.today(), None, 1, 2.0])
     result = ser.str.slice(start, stop, step)
-    expected = Series(expected)
+    expected = Series(expected, dtype=object)
     tm.assert_series_equal(result, expected)
 
 
@@ -453,7 +455,7 @@ def test_strip_lstrip_rstrip_mixed_object(method, exp):
     ser = Series(["  aa  ", np.nan, " bb \t\n", True, datetime.today(), None, 1, 2.0])
 
     result = getattr(ser.str, method)()
-    expected = Series(exp + [np.nan, np.nan, None, np.nan, np.nan])
+    expected = Series(exp + [np.nan, np.nan, None, np.nan, np.nan], dtype=object)
     tm.assert_series_equal(result, expected)
 
 
@@ -529,7 +531,7 @@ def test_string_slice_out_of_bounds(any_string_dtype):
 def test_encode_decode(any_string_dtype):
     ser = Series(["a", "b", "a\xe4"], dtype=any_string_dtype).str.encode("utf-8")
     result = ser.str.decode("utf-8")
-    expected = ser.map(lambda x: x.decode("utf-8"))
+    expected = ser.map(lambda x: x.decode("utf-8")).astype(object)
     tm.assert_series_equal(result, expected)
 
 
@@ -559,7 +561,7 @@ def test_decode_errors_kwarg():
         ser.str.decode("cp1252")
 
     result = ser.str.decode("cp1252", "ignore")
-    expected = ser.map(lambda x: x.decode("cp1252", "ignore"))
+    expected = ser.map(lambda x: x.decode("cp1252", "ignore")).astype(object)
     tm.assert_series_equal(result, expected)
 
 
@@ -672,7 +674,7 @@ def test_str_accessor_in_apply_func():
 def test_zfill():
     # https://github.com/pandas-dev/pandas/issues/20868
     value = Series(["-1", "1", "1000", 10, np.nan])
-    expected = Series(["-01", "001", "1000", np.nan, np.nan])
+    expected = Series(["-01", "001", "1000", np.nan, np.nan], dtype=object)
     tm.assert_series_equal(value.str.zfill(3), expected)
 
     value = Series(["-2", "+5"])
@@ -704,10 +706,10 @@ def test_get_with_dict_label():
         ]
     )
     result = s.str.get("name")
-    expected = Series(["Hello", "Goodbye", None])
+    expected = Series(["Hello", "Goodbye", None], dtype=object)
     tm.assert_series_equal(result, expected)
     result = s.str.get("value")
-    expected = Series(["World", "Planet", "Sea"])
+    expected = Series(["World", "Planet", "Sea"], dtype=object)
     tm.assert_series_equal(result, expected)
 
 

From ee6a0626a42d531ece2de7fefdc514123690c191 Mon Sep 17 00:00:00 2001
From: Patrick Hoefler <61934744+phofl@users.noreply.github.com>
Date: Sat, 9 Dec 2023 20:26:09 +0100
Subject: [PATCH 15/15] DEPR: Disallow dtype inference when setting Index into
 DataFrame (#56102)

---
 doc/source/whatsnew/v2.2.0.rst              |  1 +
 pandas/core/frame.py                        | 16 +++++++++++++++-
 pandas/tests/frame/indexing/test_setitem.py | 18 ++++++++++++++++++
 3 files changed, 34 insertions(+), 1 deletion(-)

diff --git a/doc/source/whatsnew/v2.2.0.rst b/doc/source/whatsnew/v2.2.0.rst
index ffefb9f41fb56..ad44e87cacf82 100644
--- a/doc/source/whatsnew/v2.2.0.rst
+++ b/doc/source/whatsnew/v2.2.0.rst
@@ -458,6 +458,7 @@ Other Deprecations
 - Deprecated behavior of :meth:`Index.insert` with an object-dtype index silently performing type inference on the result, explicitly call ``result.infer_objects(copy=False)`` for the old behavior instead (:issue:`51363`)
 - Deprecated casting non-datetimelike values (mainly strings) in :meth:`Series.isin` and :meth:`Index.isin` with ``datetime64``, ``timedelta64``, and :class:`PeriodDtype` dtypes (:issue:`53111`)
 - Deprecated downcasting behavior in :meth:`Series.where`, :meth:`DataFrame.where`, :meth:`Series.mask`, :meth:`DataFrame.mask`, :meth:`Series.clip`, :meth:`DataFrame.clip`; in a future version these will not infer object-dtype columns to non-object dtype, or all-round floats to integer dtype. Call ``result.infer_objects(copy=False)`` on the result for object inference, or explicitly cast floats to ints. To opt in to the future version, use ``pd.set_option("future.no_silent_downcasting", True)`` (:issue:`53656`)
+- Deprecated dtype inference when setting a :class:`Index` into a :class:`DataFrame`, cast explicitly instead (:issue:`56102`)
 - Deprecated including the groups in computations when using :meth:`.DataFrameGroupBy.apply` and :meth:`.DataFrameGroupBy.resample`; pass ``include_groups=False`` to exclude the groups (:issue:`7155`)
 - Deprecated indexing an :class:`Index`  with a boolean indexer of length zero (:issue:`55820`)
 - Deprecated not passing a tuple to :class:`.DataFrameGroupBy.get_group` or :class:`.SeriesGroupBy.get_group` when grouping by a length-1 list-like (:issue:`25971`)
diff --git a/pandas/core/frame.py b/pandas/core/frame.py
index 24b7951e3bb85..e741fa7b37f33 100644
--- a/pandas/core/frame.py
+++ b/pandas/core/frame.py
@@ -5219,7 +5219,21 @@ def _sanitize_column(self, value) -> tuple[ArrayLike, BlockValuesRefs | None]:
 
         if is_list_like(value):
             com.require_length_match(value, self.index)
-        return sanitize_array(value, self.index, copy=True, allow_2d=True), None
+        arr = sanitize_array(value, self.index, copy=True, allow_2d=True)
+        if (
+            isinstance(value, Index)
+            and value.dtype == "object"
+            and arr.dtype != value.dtype
+        ):  #
+            # TODO: Remove kludge in sanitize_array for string mode when enforcing
+            # this deprecation
+            warnings.warn(
+                "Setting an Index with object dtype into a DataFrame will no longer "
+                "infer another dtype. Cast the Index explicitly before setting.",
+                FutureWarning,
+                stacklevel=find_stack_level(),
+            )
+        return arr, None
 
     @property
     def _series(self):
diff --git a/pandas/tests/frame/indexing/test_setitem.py b/pandas/tests/frame/indexing/test_setitem.py
index d0caaa3756170..e802a56ecbc81 100644
--- a/pandas/tests/frame/indexing/test_setitem.py
+++ b/pandas/tests/frame/indexing/test_setitem.py
@@ -786,6 +786,24 @@ def test_loc_setitem_ea_dtype(self):
         df.iloc[:, 0] = Series([11], dtype="Int64")
         tm.assert_frame_equal(df, expected)
 
+    def test_setitem_object_inferring(self):
+        # GH#56102
+        idx = Index([Timestamp("2019-12-31")], dtype=object)
+        df = DataFrame({"a": [1]})
+        with tm.assert_produces_warning(FutureWarning, match="infer"):
+            df.loc[:, "b"] = idx
+        with tm.assert_produces_warning(FutureWarning, match="infer"):
+            df["c"] = idx
+
+        expected = DataFrame(
+            {
+                "a": [1],
+                "b": Series([Timestamp("2019-12-31")], dtype="datetime64[ns]"),
+                "c": Series([Timestamp("2019-12-31")], dtype="datetime64[ns]"),
+            }
+        )
+        tm.assert_frame_equal(df, expected)
+
 
 class TestSetitemTZAwareValues:
     @pytest.fixture