9.2 KiB
9.2 KiB
name, description, category, tags, version
| name | description | category | tags | version | |||||
|---|---|---|---|---|---|---|---|---|---|
| unit-test-application-events | Testing Spring application events (ApplicationEvent) with @EventListener and ApplicationEventPublisher. Test event publishing, listening, and async event handling in Spring Boot applications. Use when validating event-driven workflows in your Spring Boot services. | testing |
|
1.0.1 |
Unit Testing Application Events
Test Spring ApplicationEvent publishers and event listeners using JUnit 5. Verify event publishing, listener execution, and event propagation without full context startup.
When to Use This Skill
Use this skill when:
- Testing ApplicationEventPublisher event publishing
- Testing @EventListener method invocation
- Verifying event listener logic and side effects
- Testing event propagation through listeners
- Want fast event-driven architecture tests
- Testing both synchronous and asynchronous event handling
Setup: Event Testing
Maven
<dependency>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter</artifactId>
</dependency>
<dependency>
<groupId>org.junit.jupiter</groupId>
<artifactId>junit-jupiter</artifactId>
<scope>test</scope>
</dependency>
<dependency>
<groupId>org.mockito</groupId>
<artifactId>mockito-core</artifactId>
<scope>test</scope>
</dependency>
<dependency>
<groupId>org.assertj</groupId>
<artifactId>assertj-core</artifactId>
<scope>test</scope>
</dependency>
Gradle
dependencies {
implementation("org.springframework.boot:spring-boot-starter")
testImplementation("org.junit.jupiter:junit-jupiter")
testImplementation("org.mockito:mockito-core")
testImplementation("org.assertj:assertj-core")
}
Basic Pattern: Event Publishing and Listening
Custom Event and Publisher
// Custom application event
public class UserCreatedEvent extends ApplicationEvent {
private final User user;
public UserCreatedEvent(Object source, User user) {
super(source);
this.user = user;
}
public User getUser() {
return user;
}
}
// Service that publishes events
@Service
public class UserService {
private final ApplicationEventPublisher eventPublisher;
private final UserRepository userRepository;
public UserService(ApplicationEventPublisher eventPublisher, UserRepository userRepository) {
this.eventPublisher = eventPublisher;
this.userRepository = userRepository;
}
public User createUser(String name, String email) {
User user = new User(name, email);
User savedUser = userRepository.save(user);
eventPublisher.publishEvent(new UserCreatedEvent(this, savedUser));
return savedUser;
}
}
// Unit test
import org.junit.jupiter.api.Test;
import org.junit.jupiter.api.extension.ExtendWith;
import org.mockito.ArgumentCaptor;
import org.mockito.InjectMocks;
import org.mockito.Mock;
import org.mockito.junit.jupiter.MockitoExtension;
import static org.assertj.core.api.Assertions.*;
import static org.mockito.Mockito.*;
@ExtendWith(MockitoExtension.class)
class UserServiceEventTest {
@Mock
private ApplicationEventPublisher eventPublisher;
@Mock
private UserRepository userRepository;
@InjectMocks
private UserService userService;
@Test
void shouldPublishUserCreatedEvent() {
User newUser = new User(1L, "Alice", "alice@example.com");
when(userRepository.save(any(User.class))).thenReturn(newUser);
ArgumentCaptor<UserCreatedEvent> eventCaptor = ArgumentCaptor.forClass(UserCreatedEvent.class);
userService.createUser("Alice", "alice@example.com");
verify(eventPublisher).publishEvent(eventCaptor.capture());
UserCreatedEvent capturedEvent = eventCaptor.getValue();
assertThat(capturedEvent.getUser()).isEqualTo(newUser);
}
}
Testing Event Listeners
@EventListener Annotation
// Event listener
@Component
public class UserEventListener {
private final EmailService emailService;
public UserEventListener(EmailService emailService) {
this.emailService = emailService;
}
@EventListener
public void onUserCreated(UserCreatedEvent event) {
User user = event.getUser();
emailService.sendWelcomeEmail(user.getEmail());
}
}
// Unit test for listener
class UserEventListenerTest {
@Test
void shouldSendWelcomeEmailWhenUserCreated() {
EmailService emailService = mock(EmailService.class);
UserEventListener listener = new UserEventListener(emailService);
User newUser = new User(1L, "Alice", "alice@example.com");
UserCreatedEvent event = new UserCreatedEvent(this, newUser);
listener.onUserCreated(event);
verify(emailService).sendWelcomeEmail("alice@example.com");
}
@Test
void shouldNotThrowExceptionWhenEmailServiceFails() {
EmailService emailService = mock(EmailService.class);
doThrow(new RuntimeException("Email service down"))
.when(emailService).sendWelcomeEmail(any());
UserEventListener listener = new UserEventListener(emailService);
User newUser = new User(1L, "Alice", "alice@example.com");
UserCreatedEvent event = new UserCreatedEvent(this, newUser);
// Should handle exception gracefully
assertThatCode(() -> listener.onUserCreated(event))
.doesNotThrowAnyException();
}
}
Testing Multiple Listeners
Event Propagation
class UserCreatedEvent extends ApplicationEvent {
private final User user;
private final List<String> notifications = new ArrayList<>();
public UserCreatedEvent(Object source, User user) {
super(source);
this.user = user;
}
public void addNotification(String notification) {
notifications.add(notification);
}
public List<String> getNotifications() {
return notifications;
}
}
class MultiListenerTest {
@Test
void shouldNotifyMultipleListenersSequentially() {
EmailService emailService = mock(EmailService.class);
NotificationService notificationService = mock(NotificationService.class);
AnalyticsService analyticsService = mock(AnalyticsService.class);
UserEventListener emailListener = new UserEventListener(emailService);
UserEventListener notificationListener = new UserEventListener(notificationService);
UserEventListener analyticsListener = new UserEventListener(analyticsService);
User user = new User(1L, "Alice", "alice@example.com");
UserCreatedEvent event = new UserCreatedEvent(this, user);
emailListener.onUserCreated(event);
notificationListener.onUserCreated(event);
analyticsListener.onUserCreated(event);
verify(emailService).send(any());
verify(notificationService).notify(any());
verify(analyticsService).track(any());
}
}
Testing Conditional Event Listeners
@EventListener with Condition
@Component
public class ConditionalEventListener {
@EventListener(condition = "#event.user.age > 18")
public void onAdultUserCreated(UserCreatedEvent event) {
// Handle adult user
}
}
class ConditionalListenerTest {
@Test
void shouldProcessEventWhenConditionMatches() {
// Test logic for matching condition
}
@Test
void shouldSkipEventWhenConditionDoesNotMatch() {
// Test logic for non-matching condition
}
}
Testing Async Event Listeners
@Async with @EventListener
@Component
public class AsyncEventListener {
private final SlowService slowService;
@EventListener
@Async
public void onUserCreatedAsync(UserCreatedEvent event) {
slowService.processUser(event.getUser());
}
}
class AsyncEventListenerTest {
@Test
void shouldProcessEventAsynchronously() throws Exception {
SlowService slowService = mock(SlowService.class);
AsyncEventListener listener = new AsyncEventListener(slowService);
User user = new User(1L, "Alice", "alice@example.com");
UserCreatedEvent event = new UserCreatedEvent(this, user);
listener.onUserCreatedAsync(event);
// Event processed asynchronously
Thread.sleep(100); // Wait for async completion
verify(slowService).processUser(user);
}
}
Best Practices
- Mock ApplicationEventPublisher in unit tests
- Capture published events using ArgumentCaptor
- Test listener side effects explicitly
- Test error handling in listeners
- Keep event listeners focused on single responsibility
- Verify event data integrity when capturing
- Test both sync and async event processing
Common Pitfalls
- Testing actual event publishing without mocking publisher
- Not verifying listener invocation
- Not capturing event details
- Testing listener registration instead of logic
- Not handling listener exceptions
Troubleshooting
Event not being captured: Verify ArgumentCaptor type matches event class.
Listener not invoked: Ensure event is actually published and listener is registered.
Async listener timing issues: Use Thread.sleep() or Awaitility to wait for completion.