def test_bindPreservesOriginal(self):
        msg = Message.new(key=4)
        msg.bind(key=6)
        self.assertEqual(msg.contents(), {"key": 4})
L{Message.bind} does not mutate the instance it is called on.
dataset/ETHPy150Open ClusterHQ/eliot/eliot/tests/test_message.py/MessageTests.test_bindPreservesOriginal