add test for concat to preserve indices with same name

Author: iamlemec

pandas/tests/reshape/test_concat.py

@@ -1279,6 +1279,18 @@ def test_concat_ignore_index(self, sort):
 
         tm.assert_frame_equal(v1, expected)
 
+    def test_concat_same_index_names(self):
+        # GH13475
+        index1 = pd.Index(['a', 'b'], name='idx')
+        index2 = pd.Index(['b', 'c'], name='idx')
+
+        frame1 = pd.DataFrame({'x': [1, 2]}, index=index1)
+        frame2 = pd.DataFrame({'x': [2, 3]}, index=index2)
+
+        result = pd.concat([frame1, frame2], axis=1)
+
+        assert result.index.name == 'idx'
+
     def test_concat_multiindex_with_keys(self):
         index = MultiIndex(
             levels=[["foo", "bar", "baz", "qux"], ["one", "two", "three"]],