单元测试Spring ApplicationEvents - 事件是否已发布但侦听器未触发？

Question

我正在尝试对我在Spring中创建的自定义事件进行单元测试,并且遇到了一个有趣的问题.如果我创建StaticApplicationContext并手动注册并连接bean,我可以触发事件并看到程序流通过发布者(实现ApplicationEventPublisherAware)到监听器(implements ApplicationListener<?>).

然而,当我尝试创建一个JUnit测试来创建使用的上下文时SpringJunit4ClassRunner,@ContextConfiguration一切正常,除了ApplicationEvents没有出现在监听器中(我已经确认它们已经发布).

是否有其他方法来创建上下文,以便ApplicationEvents正常工作？我没有在网上找到关于单元测试Spring事件框架的内容.

Answer 1

The events will not fire because your test classes are not registered and resolved from the spring application context, which is the event publisher.

I've implemented a workaround for this where the event is handled in another class that is registered with Spring as a bean and resolved as part of the test. It isn't pretty, but after wasting the best part of a day trying to find a better solution I am happy with this for now.

My use case was firing an event when a message is received within a RabbitMQ consumer. It is made up of the following:

The wrapper class

Note the Init() function that is called from the test to pass in the callback function after resolving from the container within the test

public class TestEventListenerWrapper {

CountDownLatch countDownLatch;
TestEventWrapperCallbackFunction testEventWrapperCallbackFunction;

public TestEventListenerWrapper(){

}

public void Init(CountDownLatch countDownLatch, TestEventWrapperCallbackFunction testEventWrapperCallbackFunction){

    this.countDownLatch = countDownLatch;
    this.testEventWrapperCallbackFunction = testEventWrapperCallbackFunction;
}

@EventListener
public void onApplicationEvent(MyEventType1 event) {

    testEventWrapperCallbackFunction.CallbackOnEventFired(event);
    countDownLatch.countDown();
}

@EventListener
public void onApplicationEvent(MyEventType2 event) {

    testEventWrapperCallbackFunction.CallbackOnEventFired(event);
    countDownLatch.countDown();
}

@EventListener
public void onApplicationEvent(OnQueueMessageReceived event) {

    testEventWrapperCallbackFunction.CallbackOnEventFired(event);
    countDownLatch.countDown();
}
}

The callback interface

public interface TestEventWrapperCallbackFunction {

void CallbackOnEventFired(ApplicationEvent event);
}

A test configuration class to define the bean which is referenced in the unit test. Before this is useful, it will need to be resolved from the applicationContext and initialsed (see next step)

    @Configuration
public class TestContextConfiguration {
    @Lazy
    @Bean(name="testEventListenerWrapper")
    public TestEventListenerWrapper testEventListenerWrapper(){
        return new TestEventListenerWrapper();
    }
}

Finally, the unit test itself that resolves the bean from the applicationContext and calls the Init() function to pass assertion criteria (this assumes you have registered the bean as a singleton - the default for the Spring applicationContext). The callback function is defined here and also passed to Init().

    @ContextConfiguration(classes= {TestContextConfiguration.class,
                                //..., - other config classes
                                //..., - other config classes
                                })
public class QueueListenerUnitTests
        extends AbstractTestNGSpringContextTests {

    private MessageProcessorManager mockedMessageProcessorManager;
    private ChannelAwareMessageListener queueListener;

    private OnQueueMessageReceived currentEvent;

    @BeforeTest
    public void Startup() throws Exception {

        this.springTestContextPrepareTestInstance();
        queueListener = new QueueListenerImpl(mockedMessageProcessorManager);
        ((QueueListenerImpl) queueListener).setApplicationEventPublisher(this.applicationContext);
        currentEvent = null;
    }

    @Test
    public void HandleMessageReceived_QueueMessageReceivedEventFires_WhenValidMessageIsReceived() throws Exception {

        //Arrange
        //Other arrange logic
        Channel mockedRabbitmqChannel = CreateMockRabbitmqChannel();
        CountDownLatch countDownLatch = new CountDownLatch(1);

        TestEventWrapperCallbackFunction testEventWrapperCallbackFunction = (ev) -> CallbackOnEventFired(ev);
        TestEventListenerWrapper testEventListenerWrapper = (TestEventListenerWrapper)applicationContext.getBean("testEventWrapperOnQueueMessageReceived");
        testEventListenerWrapper.Init(countDownLatch, testEventWrapperCallbackFunction);

        //Act
        queueListener.onMessage(message, mockedRabbitmqChannel);
        long awaitTimeoutInMs = 1000;
        countDownLatch.await(awaitTimeoutInMs, TimeUnit.MILLISECONDS);

        //Assert - assertion goes here
    }

    //The callback function that passes the event back here so it can be made available to the tests for assertion
    private void CallbackOnEventFired(ApplicationEvent event){
        currentEvent = (OnQueueMessageReceived)event;
    }
}

• EDIT 1: The sample code has been updated with CountDownLatch
• EDIT 2: Assertions didn't fail tests so the above was updated with a different approach**