Java Testing Skill Write comprehensive tests for Java applications with modern testing practices. Overview This skill covers Java testing with JUnit 5, Mockito, AssertJ, and integration testing with Spring Boot Test and Testcontainers. Includes TDD patterns and test coverage strategies. When to Use This Skill Use when you need to: Write unit tests with JUnit 5 Create mocks with Mockito Build integration tests with Testcontainers Implement TDD/BDD practices Improve test coverage Topics Covered JUnit 5 @Test, @Nested, @DisplayName @ParameterizedTest with sources Lifecycle annotations Extensions and custom annotations Mockito @Mock, @InjectMocks, @Spy Stubbing (when/thenReturn) Verification (verify, times) BDD style (given/willReturn) AssertJ Fluent assertions Collection assertions Exception assertions Custom assertions Integration Testing @SpringBootTest slices Testcontainers setup MockMvc for APIs Database testing Quick Reference Test Data Builders Coverage Goals Troubleshooting Common Issues Problem Cause Solution Mock not working Missing @ExtendWith Add MockitoExtension NPE in test Mock not initialized Check @InjectMocks Flaky test Shared state Isolate test data Context fails Missing bean Use @MockBean Debug Checklist Usage Related Skills java testing advanced Advanced patterns java spring boot Spring test slices

java-testing