您可以在测试中使用CoundDownLatch并等待MessageHandler处理您的消息。您的示例如下所示：

@Test
public void testOnePojo() throws Exception {
    final CountDownLatch countDownLatch = new CountDownLatch(1);

    ExecutorChannel orderSendChannel =
        context.getBean("validationChannel", ExecutorChannel.class);
    ExecutorChannel orderReceiveChannel = context.getBean("auditChannel", ExecutorChannel.class);
    orderReceiveChannel.subscribe(t -> {
        System.out.println(t);//I want to see this output
        countDownLatch.countDown();
    });
    orderSendChannel.send(getMessageMessage());

    countDownLatch.await();
}