add test for fillna

Author: jorisvandenbossche

pandas/tests/extension/base/missing.py

@@ -122,6 +122,20 @@ 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 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)
+
+        # but with copy=False, this raises for EAs that respect the copy keyword
+        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 test_fillna_series(self, data_missing):
         fill_value = data_missing[1]
         ser = pd.Series(data_missing)

pandas/tests/extension/decimal/test_decimal.py

@@ -171,6 +171,10 @@ 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

@@ -687,6 +687,21 @@ 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 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)
+
+        # copy=False is generally not honored by ArrowExtensionArray, 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

@@ -100,6 +100,10 @@ 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_numpy.py

@@ -342,6 +342,11 @@ def test_fillna_frame(self, data_missing):
         # Non-scalar "scalar" values.
         super().test_fillna_frame(data_missing)
 
+    @skip_nested
+    def test_fillna_readonly(self, data_missing):
+        # Non-scalar "scalar" values.
+        super().test_fillna_readonly(data_missing)
+
     @skip_nested
     def test_setitem_invalid(self, data, invalid_scalar):
         # object dtype can hold anything, so doesn't raise

pandas/tests/extension/test_sparse.py

@@ -237,6 +237,19 @@ def test_isna(self, data_missing):
     def test_fillna_no_op_returns_copy(self, data, request):
         super().test_fillna_no_op_returns_copy(data)
 
+    def test_fillna_readonly(self, data_missing):
+        # copy=False keyword is not ignored by SparseArray.fillna
+        data = data_missing.copy()
+        data._readonly = True
+
+        # by default copy=True, then this works fine
+        result = data.fillna(data_missing[1])
+        assert result[0] == data_missing[1]
+
+        # copy=False is ignored -> so same result as above
+        result = data.fillna(data_missing[1], copy=False)
+        assert result[0] == data_missing[1]
+
     @pytest.mark.xfail(reason="Unsupported")
     def test_fillna_series(self, data_missing):
         # this one looks doable.

pandas/tests/extension/test_string.py

@@ -169,6 +169,25 @@ 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 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)
+
+        # copy=False is generally not honored by Arrow-backed array, 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: