Change test for 22721

Author: h-vetinari

pandas/tests/test_strings.py

@@ -3088,7 +3088,11 @@ def test_str_accessor_no_new_attributes(self):
     def test_method_on_bytes(self):
         lhs = Series(np.array(list('abc'), 'S1').astype(object))
         rhs = Series(np.array(list('def'), 'S1').astype(object))
+        if compat.PY3:
+            pytest.raises(TypeError, lhs.str.cat, rhs, sep=',')
+        else:
+            result = lhs.str.cat(rhs)
+            expected = Series(np.array(
+                ['ad', 'be', 'cf'], 'S2').astype(object))
+            tm.assert_series_equal(result, expected)
 
-        result = lhs.str.cat(rhs)
-        expected = Series(np.array(['ad', 'be', 'cf'], 'S2').astype(object))
-        tm.assert_series_equal(result, expected)