BUG: Handle mixed int/str types in Index.union

Author: pelagiavlas

pandas/tests/indexes/test_setops.py

@@ -395,6 +395,9 @@ def test_union_unequal(self, index_flat, fname, sname, expected_name):
         else:
             index = index_flat
 
+        if index.dtype == 'object':
+            index = index.astype(str)
+
         # test copy.union(subset) - need sort for unicode and string
         first = index.copy().set_names(fname)
         second = index[1:].set_names(sname)