add test

Author: jorisvandenbossche

pandas/core/generic.py

@@ -9542,6 +9542,7 @@ def _align_series(
                 join_index, lidx, ridx = self.index.join(
                     other.index, how=join, level=level, return_indexers=True
                 )
+
             if is_series:
                 left = self._reindex_indexer(join_index, lidx)
             elif lidx is None or join_index is None:

pandas/tests/series/methods/test_align.py

@@ -148,6 +148,19 @@ def test_align_periodindex(join_type):
     ts.align(ts[::2], join=join_type)
 
 
+def test_align_stringindex(any_string_dtype):
+    left = Series(range(3), index=pd.Index(["a", "b", "d"], dtype=any_string_dtype))
+    right = Series(range(3), index=pd.Index(["a", "b", "c"], dtype=any_string_dtype))
+    result_left, result_right = left.align(right)
+
+    expected_idx = pd.Index(["a", "b", "c", "d"], dtype=any_string_dtype)
+    expected_left = Series([0, 1, np.nan, 2], index=expected_idx)
+    expected_right = Series([0, 1, 2, np.nan], index=expected_idx)
+
+    tm.assert_series_equal(result_left, expected_left)
+    tm.assert_series_equal(result_right, expected_right)
+
+
 def test_align_left_fewer_levels():
     # GH#45224
     left = Series([2], index=pd.MultiIndex.from_tuples([(1, 3)], names=["a", "c"]))