add test and whatsnew

pandas-dev · Oct 30, 2023 · 6dcefdc · 6dcefdc
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diff --git a/doc/source/whatsnew/v2.1.3.rst b/doc/source/whatsnew/v2.1.3.rst
@@ -13,7 +13,7 @@ including other versions of pandas.
 
 Fixed regressions
 ~~~~~~~~~~~~~~~~~
--
+- Fixed regression in :meth:`DatetimeIndex.diff` raising ``TypeError`` (:issue:`55080`)
 -
 
 .. ---------------------------------------------------------------------------

diff --git a/pandas/tests/indexes/test_datetimelike.py b/pandas/tests/indexes/test_datetimelike.py
@@ -159,3 +159,11 @@ def test_where_cast_str(self, simple_index):
 
         result = index.where(mask, ["foo"])
         tm.assert_index_equal(result, expected)
+
+    @pytest.mark.parametrize("unit", ["ns", "us", "ms", "s"])
+    def test_diff(self, unit):
+        # GH 55080
+        dti = pd.to_datetime([10, 20, 30], unit=unit).as_unit(unit)
+        result = dti.diff(1)
+        expected = pd.TimedeltaIndex([pd.NaT, 10, 10], unit=unit).as_unit(unit)
+        tm.assert_index_equal(result, expected)