def test_contentsCopies(self):
        msg = Message.new(key="value")
        del msg.contents()["key"]
        self.assertEqual(msg.contents(), {"key": "value"})
L{Message.contents} returns a copy of the L{Message} contents.
dataset/ETHPy150Open ClusterHQ/eliot/eliot/tests/test_message.py/MessageTests.test_contentsCopies