use index.is_unique

Author: erbian

pandas/tests/indexes/common.py

@@ -942,9 +942,7 @@ def test_empty(self):
     def test_join_self(self, how):
         index = self.create_index()
         joined = index.join(index, how=how)
+        assert isinstance(joined, type(index))
 
-        if index is index.unique():
+        if index.is_unique:
             assert index is joined
-
-        else:
-            assert isinstance(joined, type(index))