为什么TestExecutionListener不能作为bean工作？

Question

Why does ApplicationListener work as a bean, while TestExecutionListener does not?

The following code shows no any messages from MyListener1 , because TestExecutionListener should be registered via @TestExecutionListeners .

@RunWith(SpringJUnit4ClassRunner.class)
@ContextConfiguration(classes = TestExecutionListenerTry._Config.class)
public class TestExecutionListenerTry {

    public static class Bean1 {
    }

    public static class Bean2 {
    }

    public static class MyListener1 implements TestExecutionListener {

        @Override
        public void beforeTestClass(TestContext testContext) throws Exception {
            System.out.println("beforeTestClass " + testContext.toString());
        }

        @Override
        public void prepareTestInstance(TestContext testContext) throws Exception {
            System.out.println("prepareTestInstance " + testContext.toString());
        }

        @Override
        public void beforeTestMethod(TestContext testContext) throws Exception {
            System.out.println("beforeTestMethod " + testContext.toString());
        }

        @Override
        public void afterTestMethod(TestContext testContext) throws Exception {
            System.out.println("afterTestMethod " + testContext.toString());
        }

        @Override
        public void afterTestClass(TestContext testContext) throws Exception {
            System.out.println("afterTestClass " + testContext.toString());
        }
    }

    public static class MyListener2 implements ApplicationListener<ContextRefreshedEvent> {
        @Override
        public void onApplicationEvent(ContextRefreshedEvent event) {
            System.out.println("ContextRefreshedEvent " + event.toString());
        }
    }

    @Configuration
    public static class _Config {

        @Bean
        public Bean1 bean1() {
            return new Bean1();
        }

        @Bean
        public Bean2 bean2() {
            return new Bean2();
        }

        @Bean
        public MyListener1 myListener1() {
            return new MyListener1();
        }

        @Bean
        public MyListener2 myListener2() {
            return new MyListener2();
        }
    }


    @Test
    public void test1() {
        System.out.println("test1()");
    }

    @Test
    public void test2() {
        System.out.println("test2()");
    }


}

Why such design difference?

Is there any bean, which can listen for tests?

Answer 1

An ApplicationContext , the container for beans, only knows how to generate and expose beans. That's more or less the limit of its functionality. It doesn't know anything about tests or test environments.

The ApplicationListener can be declared as a bean because the ApplicationContext defines various phases in its lifecycle (regardless of where its used) which the listeners can observe.

TestExecutionListener , however, is only useful in the context of running tests. This doesn't tie into anything the ApplicationContext does. In other words, only the SpringJUnit4ClassRunner cares about these listeners, as it runs the test methods.

In reality, TestExecutionListener beans probably could have been extracted from the ApplicationContext by the SpringJUnit4ClassRunner . It's a matter of separation of concerns as far as I'm concerned.