def test_startMessageSerialization(self):
        serializers = ActionType("sys:thename",
                                 [Field("key", lambda x: x, "")],
                                 [], "")._serializers
        class Logger(list):
            def write(self, msg, serializer):
                self.append(serializer)
        logger = Logger()
        action = Action(logger, "unique", TaskLevel(level=[]), "sys:thename",
                        serializers)
        action._start({"key": "value"})
        self.assertIs(logger[0], serializers.start)
The start message logged by L{Action._start} is created with the
dataset/ETHPy150Open ClusterHQ/eliot/eliot/tests/test_action.py/ActionTests.test_startMessageSerialization