def test_keep_first_or_last_instance(self, test_input):
     test_input.side_effect = ["xxxx", "first", "last"]
     first_or_last = keep_first_or_last_instance()
     self.assertEqual(first_or_last, "first")
     first_or_last = keep_first_or_last_instance()
     self.assertEqual(first_or_last, "last")
 def test_keep_first_or_last_instance(self, test_input):
     test_input.side_effect = ["xxxx", "first", "last"]
     first_or_last = keep_first_or_last_instance()
     self.assertEqual(first_or_last, "first")
     first_or_last = keep_first_or_last_instance()
     self.assertEqual(first_or_last, "last")