spring-boot-testing

Use @WebMvcTest with MockMvcTester on Spring Boot 3.2+ for AssertJ-style assertions. Mock service dependencies with @MockitoBean, then convert JSON responses to typed objects with bodyJson().convertTo() for type-safe assertions.

@WebMvcTest loads only the web layer (controllers, Jackson, security filters) and runs fast, while @SpringBootTest loads the entire application context for full integration testing. Prefer the narrowest slice that gives you confidence.

Replace @MockBean with @MockitoBean and @SpyBean with @MockitoSpyBean, as the older annotations are deprecated in Spring Boot 4. The new annotations also support mocking prototype-scoped beans via Spring Framework 7.

Testcontainers with a real database like PostgreSQL is recommended over H2 for production parity, since H2 can miss database-specific issues. Combine @DataJpaTest with @ServiceConnection and a PostgreSQLContainer for accurate results.

Slow suites usually come from overusing @SpringBootTest or creating many distinct context configurations. Group tests by configuration, minimize @TestPropertySource variations, avoid @DirtiesContext, and use narrow test slices to improve context cache hits.

Use Instancio when objects have three or more properties to avoid repetitive builder or setter calls. It generates fully populated objects with random data while letting you set only the fields relevant to your test scenario.