为什么添加thread.sleep会使我的AKKA测试套件单元测试通过?

爪哇8和阿卡 应用程序接口 )2.12:2.5.16此处。我有以下信息:

public class SomeMessage {
    private int anotherNum;

    public SomeMessage(int anotherNum) {
        this.anotherNum = anotherNum;
    }

    public int getAnotherNum() {
        return anotherNum;
    }

    public void setAnotherNum(int anotherNum) {
        this.anotherNum = anotherNum;
    }
}

以及以下演员:

public class TestActor extends AbstractActor {
    private Integer number;

    public TestActor(Integer number) {
        this.number = number;
    }

    @Override
    public Receive createReceive() {
        return receiveBuilder()
            .matchAny(message -> {
                if (message instanceof SomeMessage) {
                    SomeMessage someMessage = (SomeMessage) message;
                    System.out.println("someMessage contains = " + someMessage.getAnotherNum());
                    someMessage.setAnotherNum(number);
                }
            }).build();
    }
}

以及以下单元测试:

@RunWith(MockitoJUnitRunner.class)
public class TestActorTest {
    static ActorSystem actorSystem;

    @BeforeClass
    public static void setup() {
        actorSystem = ActorSystem.create();
    }

    @AfterClass
    public static void teardown() {
        TestKit.shutdownActorSystem(actorSystem, Duration.create("10 seconds"), true);
        actorSystem = null;
    }

    @Test
    public void should_alter_some_message() {
        // given
        ActorRef testActor = actorSystem.actorOf(Props.create(TestActor.class, 10), "test.actor");
        SomeMessage someMessage = new SomeMessage(5);

        // when
        testActor.tell(someMessage, ActorRef.noSender());

        // then
        assertEquals(10, someMessage.getAnotherNum());
    }
}

所以我想验证的是 TestActor 实际上是否收到 SomeMessage 它改变了它的内部状态。

当我运行这个单元测试时,它失败了,好像演员从未收到消息:

java.lang.AssertionError: 
Expected :10
Actual   :5
 <Click to see difference>

    at org.junit.Assert.fail(Assert.java:88)
    at org.junit.Assert.failNotEquals(Assert.java:834)
    at org.junit.Assert.assertEquals(Assert.java:645)
  <rest of trace omitted for brevity>

[INFO] [01/30/2019 12:50:26.780] [default-akka.actor.default-dispatcher-2] [akka://default/user/test.actor] Message [myapp.actors.core.SomeMessage] without sender to Actor[akka://default/user/test.actor#2008219661] was not delivered. [1] dead letters encountered. If this is not an expected behavior, then [Actor[akka://default/user/test.actor#2008219661]] may have terminated unexpectedly, This logging can be turned off or adjusted with configuration settings 'akka.log-dead-letters' and 'akka.log-dead-letters-during-shutdown'.

但当我修改测试方法并引入 Thread.sleep(5000) (在 tell(...) )它以飞扬的色彩通过:

@Test
public void should_alter_some_message() throws InterruptedException {
    // given
    ActorRef testActor = actorSystem.actorOf(Props.create(TestActor.class, null, 10), "test.actor");
    SomeMessage someMessage = new SomeMessage(5);

    // when
    testActor.tell(someMessage, ActorRef.noSender());

    Thread.sleep(5000);

    // then
    assertEquals(10, someMessage.getAnotherNum());
}

这是怎么回事?! 很明显我不想我的演员考试乱七八糟 sleeps ,那么我在这里做错了什么?解决方法是什么?事先谢谢!