This is a comprehensive testing guide for Spring Boot 4 that actually tells you which annotation to use when. It's built around the test pyramid and includes decision trees for choosing between @WebMvcTest, @DataJpaTest, @RestClientTest, and friends. The best part is the practical coverage: it shows you MockMvcTester (the new AssertJ-style API), Testcontainers for real database tests, and Instancio for generating test data. It also covers the Spring Boot 4 migration path from deprecated @MockBean to @MockitoBean. The complexity assessment section is refreshingly honest about when to refactor instead of writing 50 test cases for a god method. If you're moving to Spring Boot 4 or just tired of guessing which test slice to use, this gets you unstuck fast.
npx skills add https://github.com/marcelorodrigo/agent-skills --skill spring-boot-testing