combine_first with mix tz test GH#26283 (#52294)

Signed-off-by: Liang Yan <[email protected]>

Author: liang3zy22

pandas/tests/series/methods/test_combine_first.py

@@ -120,3 +120,26 @@ def test_combine_first_preserves_dtype(self):
         result = s1.combine_first(s2)
         expected = Series([1666880195890293744, 1666880195890293837, 3])
         tm.assert_series_equal(result, expected)
+
+    def test_combine_mixed_timezone(self):
+        # GH 26283
+        uniform_tz = Series({pd.Timestamp("2019-05-01", tz="UTC"): 1.0})
+        multi_tz = Series(
+            {
+                pd.Timestamp("2019-05-01 01:00:00+0100", tz="Europe/London"): 2.0,
+                pd.Timestamp("2019-05-02", tz="UTC"): 3.0,
+            }
+        )
+
+        result = uniform_tz.combine_first(multi_tz)
+        expected = Series(
+            [1.0, 3.0],
+            index=pd.Index(
+                [
+                    pd.Timestamp("2019-05-01 00:00:00+00:00", tz="UTC"),
+                    pd.Timestamp("2019-05-02 00:00:00+00:00", tz="UTC"),
+                ],
+                dtype="object",
+            ),
+        )
+        tm.assert_series_equal(result, expected)