def test_bindOverwrites(self):
        msg = Message.new(key="value", another=2)
        another = msg.bind(another=3, more=4)
        self.assertIsInstance(another, Message)
        self.assertEqual(another.contents(), {"key": "value", "another": 3,
                                              "more": 4})
L{Message.bind} returns a new L{Message} whose contents include the
dataset/ETHPy150Open ClusterHQ/eliot/eliot/tests/test_message.py/MessageTests.test_bindOverwrites