EA attribute specifying whether copy=False is ignored

Author: Aniketsy

pandas/tests/extension/base/missing.py

@@ -129,11 +129,11 @@ def test_fillna_readonly(self, data_missing):
         data = data_missing.copy()
         data._readonly = True
 
-        expected = data_missing.fillna(fill_value, copy=True)
-
         # by default fillna(copy=True), then this works fine
         res_copy = data.fillna(fill_value, copy=True)
-        tm.assert_extension_array_equal(res_copy, expected)
+        tm.assert_extension_array_equal(
+            res_copy, data_missing.fillna(fill_value, copy=True)
+        )
         tm.assert_extension_array_equal(data, data_missing)
 
         if self._supports_fillna_copy_false:
@@ -142,6 +142,7 @@ def test_fillna_readonly(self, data_missing):
                 data.fillna(fill_value, copy=False)
             tm.assert_extension_array_equal(data, data_missing)
         else:
+            # EAs that do not respect the copy keyword, copy=False is ignored
             res_no_copy = data.fillna(fill_value, copy=False)
             tm.assert_extension_array_equal(res_no_copy, res_copy)
             tm.assert_extension_array_equal(data, data_missing)

pandas/tests/extension/decimal/test_decimal.py

@@ -171,10 +171,6 @@ def test_fillna_limit_series(self, data_missing):
         ):
             super().test_fillna_limit_series(data_missing)
 
-    @pytest.mark.xfail(reason="copy keyword is missing")
-    def test_fillna_readonly(self, data_missing):
-        super().test_fillna_readonly(data_missing)
-
     def test_series_repr(self, data):
         # Overriding this base test to explicitly test that
         # the custom _formatter is used

pandas/tests/extension/test_arrow.py

@@ -687,21 +687,6 @@ def test_fillna_no_op_returns_copy(self, data):
         assert result is not data
         tm.assert_extension_array_equal(result, data)
 
-    def test_fillna_readonly(self, data_missing):
-        data = data_missing.copy()
-        data._readonly = True
-
-        # by default fillna(copy=True), then this works fine
-        result = data.fillna(data_missing[1])
-        assert result[0] == data_missing[1]
-        tm.assert_extension_array_equal(data, data_missing)
-
-        # fillna(copy=False) is generally not honored by Arrow-backed array,
-        # but always returns new data -> same result as above
-        result = data.fillna(data_missing[1])
-        assert result[0] == data_missing[1]
-        tm.assert_extension_array_equal(data, data_missing)
-
     @pytest.mark.xfail(
         reason="GH 45419: pyarrow.ChunkedArray does not support views", run=False
     )

pandas/tests/extension/test_interval.py

@@ -100,10 +100,6 @@ def test_fillna_limit_series(self, data_missing):
     def test_fillna_length_mismatch(self, data_missing):
         super().test_fillna_length_mismatch(data_missing)
 
-    @pytest.mark.xfail(reason="copy=False is not Implemented")
-    def test_fillna_readonly(self, data_missing):
-        super().test_fillna_readonly(data_missing)
-
     @pytest.mark.filterwarnings(
         "ignore:invalid value encountered in cast:RuntimeWarning"
     )

pandas/tests/extension/test_string.py

@@ -169,25 +169,6 @@ def test_fillna_no_op_returns_copy(self, data):
         assert result is not data
         tm.assert_extension_array_equal(result, data)
 
-    def test_fillna_readonly(self, data_missing):
-        data = data_missing.copy()
-        data._readonly = True
-
-        # by default fillna(copy=True), then this works fine
-        result = data.fillna(data_missing[1])
-        assert result[0] == data_missing[1]
-        tm.assert_extension_array_equal(data, data_missing)
-
-        # fillna(copy=False) is generally not honored by Arrow-backed array,
-        # but always returns new data -> same result as above
-        if data.dtype.storage == "pyarrow":
-            result = data.fillna(data_missing[1])
-            assert result[0] == data_missing[1]
-        else:
-            with pytest.raises(ValueError, match="Cannot modify read-only array"):
-                data.fillna(data_missing[1], copy=False)
-        tm.assert_extension_array_equal(data, data_missing)
-
     def _get_expected_exception(
         self, op_name: str, obj, other
     ) -> type[Exception] | tuple[type[Exception], ...] | None: