Added extra testcase

Author: shubham11941140

pandas/core/internals/blocks.py

@@ -731,12 +731,7 @@ def _replace_regex(
         replace_regex(new_values, rx, value, mask)
 
         block = self.make_block(new_values)
-        if (self.ndim == 1 or self.shape[0] == 1) or (
-            self.ndim == 2 and self.shape[0] != 1
-        ):
-            return block.convert(numeric=False, copy=False)
-        else:
-            return [block]
+        return block.convert(numeric=False, copy=False)
 
     @final
     def replace_list(

pandas/tests/frame/methods/test_replace.py

@@ -1506,7 +1506,13 @@ def test_regex_replace_scalar(
 
     @pytest.mark.parametrize("regex", [False, True])
     def test_replace_regex_dtype_frame(self, regex):
-        df = DataFrame({"A": ["0"], "B": ["0"]})
-        expected = DataFrame({"A": [1], "B": [1]})
-        result = df.replace(to_replace="0", value=1, regex=regex)
-        tm.assert_frame_equal(result, expected)
+        # GH-48644
+        df1 = DataFrame({"A": ["0"], "B": ["0"]})
+        expected_df1 = DataFrame({"A": [1], "B": [1]})
+        result_df1 = df1.replace(to_replace="0", value=1, regex=regex)
+        tm.assert_frame_equal(result_df1, expected_df1)
+
+        df2 = DataFrame({"A": ["0"], "B": [np.NaN]})
+        expected_df2 = DataFrame({"A": [1], "B": [np.NaN]})
+        result_df2 = df2.replace(to_replace="0", value=1, regex=regex)
+        tm.assert_frame_equal(result_df2, expected_df2)

pandas/tests/series/methods/test_replace.py

@@ -516,7 +516,7 @@ def test_pandas_replace_na(self):
         tm.assert_series_equal(result, exp)
 
     @pytest.mark.parametrize("regex", [False, True])
-    def test_replace_regex_dtype(self, regex):
+    def test_replace_regex_dtype_series(self, regex):
         # GH-48644
         series = pd.Series(["0"])
         expected = pd.Series([1])