def send(self, tx=None):
        if tx is not None:
            self.tx = tx  # always last transmitted msg/pkt/data
        if self.tx is None:
            raise ValueError("{0}: {1} Cannot send. No .tx."
                                "\n".format(self.stack.name,
                                            self.name))
Test whether all callback keys are created for model callback registry
dataset/ETHPy150Open ioflo/ioflo/ioflo/aio/proto/exchanging.py/Exchange.send--crossover with--dataset/ETHPy150Open linkyndy/remodel/tests/test_models.py/ModelTests.test_callback_keys