What problem does it solve? Spring Boot test suites often mix test levels, mock the wrong boundaries, or silently skip integration coverage, leaving production behavior unproven. This Skill defines a consistent testing standard covering scenario selection, test scope, fixtures, isolation, and execution for Java 21+ Spring Boot 3 and 4 applications. ## Core Features & Use Cases - Layered test strategy: Distinguishes Spring-free unit tests, @WebMvcTest controller slices, @DataJpaTest persistence slices, and full @SpringBootTest integration tests, with rules for what each level must and must not prove. - Real infrastructure integration testing: Enforces Testcontainers with the production database engine, migration-tool-built schemas, deterministic cleanup, and real security filter chains with valid credentials instead of @WithMockUser shortcuts. - Scheduler and generation-aware guidance: Covers scheduled job tests at both unit and integration levels, plus the Spring Boot 3 vs 4 differences in test starters, MockMvc auto-configuration, and RestTestClient vs TestRestTemplate. - Use Case: When adding a new REST endpoint, apply this Skill to create the controller slice test, the service unit tests, and a database-backed integration test that verifies committed state and the error contract. ## Quick Start Use the spring-boot-testing skill to write the required unit, MVC slice, and integration tests for the new UserController registration endpoint.
