[FIXED] How to test event listener in spring-boot

Issue

I am trying to test an event listener like this one

@Component
class EventHandler {
     @EventListener
    fun handler(event: SomeEvent) {      //SomeEvent is has properties source and someObject
        ...
    }
}

My test is in this format

@SpringBootTest
class SendWelcomeEmailTest {
    @Autowired
    lateinit var publisher: ApplicationEventPublisher
    
    @Test
    fun test(){
        val someObject = SomeObject()
        val event = SomeEvent(this, someObject)
        val listener = mockkClass(EventHandler::class)

        publisher.publishEvent(event)
        verify { listener.handler(any()) }
    }
}

When I run this test I am getting an

java.lang.AssertionError: Verification failed: call 1 of 1: EventHandler(#4).handler(matcher<SomeEvent>())) was not called

error, however by using debugger I can see that handler function is entered with correct parameters. So why doesn't verify catch the execution of handler function?

Solution

So with springmockk:

Gradle:

testImplementation("com.ninja-squad:springmockk:3.1.1")

Maven:

<dependency>
 <groupId>com.ninja-squad</groupId>
 <artifactId>springmockk</artifactId>
 <version>3.1.1</version>
 <scope>test</scope>
</dependency>

This test:

@SpringBootTest
class SendWelcomeEmailTest {
  @Autowired
  lateinit var publisher: ApplicationEventPublisher
  @MockkBean(relaxed = true)// strict by default!
  private lateinit var listenerMock: EventHandler
  @Test
  fun test() {
    
    val someObject = SomeObject()
    val event = SomeEvent(this, someObject)
    
    publisher.publishEvent(event)

    verify { listenerMock.handler(any()) }
  }
}

..should pass!

Please also consider:

If you want to make sure Mockito (and the standard MockBean and SpyBean annotations) is not used, you can also exclude the mockito dependency:

testImplementation("org.springframework.boot:spring-boot-starter-test") { exclude(module = "mockito-core")}

...limitations, compatibility.

Answered By - xerx593
Answer Checked By - Senaida (JavaFixing Volunteer)