Add tests in methods.py

pandas/tests/extension/base/methods.py

@@ -105,6 +105,30 @@ def test_factorize_equivalence(self, data_for_grouping, na_sentinel):
         tm.assert_numpy_array_equal(l1, l2)
         self.assert_extension_array_equal(u1, u2)
 
+    def test_fillna_copy_frame(self, data_missing):
+        arr = data_missing.take([1, 1])
+        df = pd.DataFrame({"A": arr})
+
+        filled_val = df.iloc[0, 0]
+        result = df.fillna(filled_val)
+
+        assert df.A.values is not result.A.values
+
+    def test_fillna_copy_series(self, data_missing):
+        arr = data_missing.take([1, 1])
+        ser = pd.Series(arr)
+
+        filled_val = ser[0]
+        result = ser.fillna(filled_val)
+
+        assert ser._values is not result._values
+        assert ser._values is arr
+
+    def test_fillna_length_mismatch(self, data_missing):
+        with (tm.assert_raises_regex(ValueError,
+              "Length of 'value' does not match.")):
+            data_missing.fillna(data_missing.take([1]))
+
     def test_combine_le(self, data_repeated):
         # GH 20825
         # Test that combine works when doing a <= (le) comparison

pandas/tests/extension/test_categorical.py

@@ -191,6 +191,10 @@ def test_combine_add(self, data_repeated):
         expected = pd.Series([a + val for a in list(orig_data1)])
         self.assert_series_equal(result, expected)
 
+    @pytest.mark.skip(reason="Not Applicable")
+    def test_fillna_length_mismatch(self, data_missing):
+        pass
+
 
 class TestCasting(base.BaseCastingTests):
     pass

pandas/tests/extension/test_interval.py

@@ -109,6 +109,10 @@ class TestMethods(BaseInterval, base.BaseMethodsTests):
     def test_combine_add(self, data_repeated):
         pass
 
+    @pytest.mark.skip(reason="Not Applicable")
+    def test_fillna_length_mismatch(self, data_missing):
+        pass
+
 
 class TestMissing(BaseInterval, base.BaseMissingTests):
     # Index.fillna only accepts scalar `value`, so we have to skip all

pandas/tests/extension/test_sparse.py

@@ -231,6 +231,30 @@ def test_combine_le(self, data_repeated):
         ], fill_value=False))
         self.assert_series_equal(result, expected)
 
+    def test_fillna_copy_frame(self, data_missing):
+        arr = data_missing.take([1, 1])
+        df = pd.DataFrame({"A": arr})
+
+        filled_val = df.iloc[0, 0]
+        result = df.fillna(filled_val)
+
+        assert df.values.base is not result.values.base
+        assert df.A._values.to_dense() is arr.to_dense()
+
+    def test_fillna_copy_series(self, data_missing):
+        arr = data_missing.take([1, 1])
+        ser = pd.Series(arr)
+
+        filled_val = ser[0]
+        result = ser.fillna(filled_val)
+
+        assert ser._values is not result._values
+        assert ser._values.to_dense() is arr.to_dense()
+
+    @pytest.mark.skip(reason="Not Applicable")
+    def test_fillna_length_mismatch(self, data_missing):
+        pass
+
 
 class TestCasting(BaseSparseTests, base.BaseCastingTests):
     pass