Fix arrow string test

Author: snitish

pandas/core/reshape/merge.py

@@ -1032,6 +1032,7 @@ def __init__(
         if validate is not None:
             self._validate_validate_kwd(validate)
 
+    @final
     def _validate_how(
         self, how: JoinHow | Literal["left_anti", "right_anti", "asof"]
     ) -> tuple[JoinHow | Literal["asof"], bool]:

pandas/tests/reshape/merge/test_merge_antijoin.py

@@ -36,7 +36,7 @@ def test_merge_antijoin_on_different_columns(self):
                 "A": [3.0],
                 "B": ["c"],
                 "C": [np.nan],
-                "D": np.array([np.nan], dtype=object),
+                "D": np.array([np.nan], dtype=right.D.dtype),
             },
             index=[2],
         )
@@ -46,7 +46,7 @@ def test_merge_antijoin_on_different_columns(self):
         expected = DataFrame(
             {
                 "A": [np.nan],
-                "B": np.array([np.nan], dtype=object),
+                "B": np.array([np.nan], dtype=left.B.dtype),
                 "C": [2.0],
                 "D": ["d"],
             },
@@ -64,7 +64,7 @@ def test_merge_antijoin_nonunique_keys(self):
                 "A": [1.0],
                 "B": ["a"],
                 "C": [np.nan],
-                "D": np.array([np.nan], dtype=object),
+                "D": np.array([np.nan], dtype=right.D.dtype),
             },
             index=[0],
         )
@@ -74,7 +74,7 @@ def test_merge_antijoin_nonunique_keys(self):
         expected = DataFrame(
             {
                 "A": [np.nan, np.nan],
-                "B": np.array([np.nan, np.nan], dtype=object),
+                "B": np.array([np.nan, np.nan], dtype=left.B.dtype),
                 "C": [2.0, 4.0],
                 "D": ["d", "d"],
             },
@@ -93,7 +93,7 @@ def test_merge_antijoin_nans(self):
         right = DataFrame({"A": [3.0, 2.0, np.nan], "D": ["d", "e", "f"]})
         result = merge(left, right, how="left_anti", on="A")
         expected = DataFrame(
-            {"A": [1.0], "C": ["a"], "D": np.array([np.nan], dtype=object)}
+            {"A": [1.0], "C": ["a"], "D": np.array([np.nan], dtype=right.D.dtype)}
         )
         tm.assert_frame_equal(result, expected)