RocketMQ是我们常用的消息中间件，在运行单元测试时，我们可能不需要真正发送消息（除非是为了测试发送消息），也不想因为连结不上RocketMQ的Broker,NameServer而影响单元测试运行。
那我们该如何Mock RocketMQ消息生产者呢？
请看例子：

//RocketMQ消息生产者 Mock 

public class RocetMQProducerMockingTest {
    // 把RocketMQ的生产者mock
    @BeforeClass
    public static void mockRocketMQ() {
        new RocketMQProducerMockUp();
    }

    @Test
    public void testSendRocketMQMessage() throws Exception {
        DefaultMQProducer producer = new DefaultMQProducer("test_producer");
        producer.setNamesrvAddr("192.168.0.2:9876;192.168.0.3:9876");
        producer.start();
        for (int i = 0; i < 20; i++) {
            Message msg = new Message("testtopic", "TagA", ("Hello " + i).getBytes());
            // 因为mq生产者已经mock,所以消息并不会真正的发送，即使nameServer连不上，也不影响单元测试的运行
            SendResult result = producer.send(msg);
            Assert.isTrue(result.getSendStatus() == SendStatus.SEND_OK);
            Assert.isTrue(result.getMsgId() != null);
        }
        producer.shutdown();
    }
}

最关键的类是RocketMQProducerMockUp，这个类改变了生产者默认实现。代码如下：

//MQ消息发送者 的MockUp(伪类） 
public class RocketMQProducerMockUp extends MockUp<DefaultMQProducer> {

    @Mock
    void init() throws MQClientException {
        // 构造函数也什么都不做
    }

    @Mock
    void start() throws MQClientException {
        // 启动，什么都不做 
    }

    @Mock
    void shutdown() {
        // 关闭，也什么都不做 
    }

    @Mock
    List<MessageQueue> fetchPublishMessageQueues(final String topic) throws MQClientException {
        // 欺骗调用方，返回不存在的消息队列，因为消息并不会真正发送嘛
        List<MessageQueue> queues = new ArrayList<MessageQueue>();
        MessageQueue q = new MessageQueue();
        q.setBrokerName("testbrokername");
        q.setQueueId(1);
        q.setTopic("testtopic");
        queues.add(q);
        return queues;
    }

    // 下面是对各个send方法的mock,都返回消息成功结果
    @Mock
    SendResult send(final Message msg)
            throws MQClientException, RemotingException, MQBrokerException, InterruptedException {
        return newSuccessSendResult();
    }

    @Mock
    SendResult send(final Message msg, final long timeout)
            throws MQClientException, RemotingException, MQBrokerException, InterruptedException {
        return newSuccessSendResult();
    }

    @Mock
    void send(final Message msg, final SendCallback sendCallback)
            throws MQClientException, RemotingException, InterruptedException {
        sendCallback.onSuccess(this.newSuccessSendResult());
    }

    @Mock
    void send(final Message msg, final SendCallback sendCallback, final long timeout)
            throws MQClientException, RemotingException, InterruptedException {
        sendCallback.onSuccess(this.newSuccessSendResult());
    }

    @Mock
    void sendOneway(final Message msg) throws MQClientException, RemotingException, InterruptedException {

    }

    @Mock
    SendResult send(final Message msg, final MessageQueue mq)
            throws MQClientException, RemotingException, MQBrokerException, InterruptedException {
        return newSuccessSendResult();
    }

    @Mock
    SendResult send(final Message msg, final MessageQueue mq, final long timeout)
            throws MQClientException, RemotingException, MQBrokerException, InterruptedException {
        return newSuccessSendResult();
    }

    @Mock
    void send(final Message msg, final MessageQueue mq, final SendCallback sendCallback)
            throws MQClientException, RemotingException, InterruptedException {
        sendCallback.onSuccess(this.newSuccessSendResult());
    }

    @Mock
    void send(final Message msg, final MessageQueue mq, final SendCallback sendCallback, long timeout)
            throws MQClientException, RemotingException, InterruptedException {
        sendCallback.onSuccess(this.newSuccessSendResult());
    }

    @Mock
    void sendOneway(final Message msg, final MessageQueue mq)
            throws MQClientException, RemotingException, InterruptedException {

    }

    @Mock
    SendResult send(final Message msg, final MessageQueueSelector selector, final Object arg)
            throws MQClientException, RemotingException, MQBrokerException, InterruptedException {
        return newSuccessSendResult();
    }

    @Mock
    SendResult send(final Message msg, final MessageQueueSelector selector, final Object arg, final long timeout)
            throws MQClientException, RemotingException, MQBrokerException, InterruptedException {
        return newSuccessSendResult();
    }

    @Mock
    void send(final Message msg, final MessageQueueSelector selector, final Object arg, final SendCallback sendCallback)
            throws MQClientException, RemotingException, InterruptedException {
        sendCallback.onSuccess(this.newSuccessSendResult());
    }

    @Mock
    void send(final Message msg, final MessageQueueSelector selector, final Object arg, final SendCallback sendCallback,
            final long timeout) throws MQClientException, RemotingException, InterruptedException {
        sendCallback.onSuccess(this.newSuccessSendResult());
    }

    @Mock
    void sendOneway(final Message msg, final MessageQueueSelector selector, final Object arg)
            throws MQClientException, RemotingException, InterruptedException {

    }

    @Mock
    TransactionSendResult sendMessageInTransaction(final Message msg, final LocalTransactionExecuter tranExecuter,
            final Object arg) throws MQClientException {
        return newTransactionSendResult();
    }

    private TransactionSendResult newTransactionSendResult() {
        TransactionSendResult success = new TransactionSendResult();
        success.setSendStatus(SendStatus.SEND_OK);
        success.setMsgId(UUID.randomUUID().toString());
        MessageQueue q = new MessageQueue();
        q.setBrokerName("testbrokername");
        q.setQueueId(1);
        q.setTopic("testtopic");
        success.setMessageQueue(q);
        success.setLocalTransactionState(LocalTransactionState.COMMIT_MESSAGE);
        return success;
    }

    private SendResult newSuccessSendResult() {
        SendResult success = new SendResult();
        success.setSendStatus(SendStatus.SEND_OK);
        success.setMsgId(UUID.randomUUID().toString());
        MessageQueue q = new MessageQueue();
        q.setBrokerName("testbrokername");
        q.setQueueId(1);
        q.setTopic("testtopic");
        success.setMessageQueue(q);
        return success;
    }
}