diff --git a/pandas/core/config_init.py b/pandas/core/config_init.py
index a8b63f97141c2..ff7064b760d88 100644
--- a/pandas/core/config_init.py
+++ b/pandas/core/config_init.py
@@ -476,9 +476,7 @@ def use_inf_as_na_cb(key) -> None:
         "copy_on_write",
         # Get the default from an environment variable, if set, otherwise defaults
         # to False. This environment variable can be set for testing.
-        "warn"
-        if os.environ.get("PANDAS_COPY_ON_WRITE", "0") == "warn"
-        else os.environ.get("PANDAS_COPY_ON_WRITE", "0") == "1",
+        "warn",
         copy_on_write_doc,
         validator=is_one_of_factory([True, False, "warn"]),
     )
diff --git a/pandas/tests/apply/test_invalid_arg.py b/pandas/tests/apply/test_invalid_arg.py
index 80b2cce8c1dbc..b10b8503c9220 100644
--- a/pandas/tests/apply/test_invalid_arg.py
+++ b/pandas/tests/apply/test_invalid_arg.py
@@ -149,7 +149,7 @@ def test_transform_axis_1_raises():
         Series([1]).transform("sum", axis=1)
 
 
-def test_apply_modify_traceback():
+def test_apply_modify_traceback(warn_copy_on_write):
     data = DataFrame(
         {
             "A": [
@@ -206,7 +206,8 @@ def transform(row):
 
     msg = "'float' object has no attribute 'startswith'"
     with pytest.raises(AttributeError, match=msg):
-        data.apply(transform, axis=1)
+        with tm.assert_cow_warning(warn_copy_on_write):
+            data.apply(transform, axis=1)
 
 
 @pytest.mark.parametrize(