spring-testing-fundamentals

Spring Testing Fundamentals

Signals: assertThat, assertThatThrownBy, given/willReturn, then(mock).should, ArgumentCaptor, @MockitoBean, @MockitoSpyBean, @DirtiesContext, context caching, testing pyramid

Tested With

• Spring Boot 3.2+ / Spring Boot 4.x
• Spring Framework 6.x / Spring Framework 7.x
• AssertJ 3.24+
• Mockito 5.x
• JUnit 5

Do NOT Use This Skill When

You need domain-specific patterns:

• Testing JPA repositories, Testcontainers, @DataJpaTest → use spring-jpa-testing
• Testing REST controllers, MockMvc, @WebMvcTest → use spring-mvc-testing
• Testing security, @WithMockUser, JWT, OAuth2 → use spring-security-testing
• Testing reactive controllers, @WebFluxTest, StepVerifier → use spring-webflux-testing
• Testing WebSocket/STOMP → use spring-websocket-testing

When to Read References

Situation	Read
AssertJ scalars, optionals, BigDecimal, collections, exceptions	references/assertj-mockito-idioms.md
BDDMockito given/willReturn, then(mock).should, argument matchers	references/assertj-mockito-idioms.md
ArgumentCaptor usage and verification patterns	references/assertj-mockito-idioms.md
UnnecessaryStubbingException and strict stubbing fixes	references/assertj-mockito-idioms.md
@MockitoBean vs @MockitoSpyBean in Boot 4	references/assertj-mockito-idioms.md
Testing pyramid: when to use each slice annotation	references/cross-cutting-testing-patterns.md
Context caching: why tests are slow, cache key, @DirtiesContext impact	references/cross-cutting-testing-patterns.md
Universal anti-patterns across all Spring test types	references/cross-cutting-testing-patterns.md
Boot 4 annotation migration checklist	references/cross-cutting-testing-patterns.md