### Question:
SequenceProducerImpl extends AbstractOMSProducer implements SequenceProducer { @Override public synchronized void rollback() { msgCacheQueue.clear(); } SequenceProducerImpl(final KeyValue properties); @Override KeyValue properties(); @Override void send(final Message message); @Override void send(final Message message, final KeyValue properties); @Override synchronized void commit(); @Override synchronized void rollback();  }### Answer:
@Test public void testRollback() { when(rocketmqProducer.getMaxMessageSize()).thenReturn(1024); final BytesMessage message = producer.createBytesMessageToTopic("HELLO_TOPIC", new byte[] {'a'}); producer.send(message); producer.rollback(); producer.commit(); assertThat(message.headers().getString(MessageHeader.MESSAGE_ID)).isEqualTo(null); }