TST: Check map function works with StringDType (pandas-dev#40823).

Author: mdhsieh

pandas/tests/frame/methods/test_map.py

@@ -0,0 +1,33 @@
+import numpy as np
+import pytest
+
+import pandas as pd
+import pandas._testing as tm
+
+
+class TestMap:
+    def test_map(self):
+        # map test on StringDType, GH#40823
+        df1 = pd.DataFrame(
+            {
+                "col1": [pd.NA, "foo", "bar"]
+            }, index=["id1", "id2", "id3"], dtype=pd.StringDtype()
+        )
+
+        df2 = pd.DataFrame(
+            {
+                "id": ["id4", "id2", "id1"]
+            }, dtype=pd.StringDtype()
+        )
+        
+        df2["col1"] = df2["id"].map(df1["col1"])
+        
+        result = df2
+        expected = pd.DataFrame(
+            {
+                "id": ["id4", "id2", "id1"], 
+                "col1": [pd.NA, "foo", pd.NA]
+            }, dtype=pd.StringDtype()
+        )
+        
+        tm.assert_frame_equal(result, expected)