Unit Testing Application Events

Overview

Provides actionable patterns for testing Spring ApplicationEvent publishers and @EventListener consumers using JUnit 5 and Mockito — without booting the full Spring context.

When to Use

• Writing unit tests for event publishers or listeners
• Verifying that an event was published with correct payload
• Testing @EventListener method invocation and side effects
• Testing event propagation through multiple listeners
• Validating async event handling (@Async + @EventListener)
• Mocking ApplicationEventPublisher in service tests

Instructions

1. Add test dependencies: spring-boot-starter, JUnit 5, Mockito, AssertJ
2. Mock ApplicationEventPublisher: use @Mock on the publisher field in the service under test