spring-boot-testing

name	spring-boot-testing
description	Spring Boot 4 testing strategies and patterns. Use when writing unit tests, slice tests (@WebMvcTest, @DataJpaTest), integration tests, Testcontainers with @ServiceConnection, security testing (@WithMockUser, JWT), or Modulith event testing with Scenario API. Covers the critical @MockitoBean migration from @MockBean.

Spring Boot 4 Testing

Comprehensive testing patterns including slice tests, Testcontainers, security testing, and Modulith Scenario API.

Critical Breaking Change

Old (Boot 3.x)	New (Boot 4.x)	Notes
@MockBean	@MockitoBean	Required migration
@SpyBean	@MockitoSpyBean	Required migration
Implicit @AutoConfigureMockMvc	Explicit annotation required	Add to @SpringBootTest

Test Annotation Selection

Test Type	Annotation	Use When
Controller	@WebMvcTest	Testing request/response, validation
Repository	@DataJpaTest	Testing queries, entity mapping
JSON	@JsonTest	Testing serialization/deserialization
REST Client	@RestClientTest	Testing external API clients
Full Integration	@SpringBootTest	End-to-end, with real dependencies
Module	@ApplicationModuleTest	Testing bounded context in isolation

Core Workflow

1. Choose test slice → Minimal context for fast tests
2. Mock dependencies → @MockitoBean for external services
3. Use Testcontainers → @ServiceConnection for databases
4. Assert thoroughly → Use AssertJ, MockMvcTester, WebTestClient
5. Test security → @WithMockUser, JWT mocking

Quick Patterns

See EXAMPLES.md for complete working examples including:

• @WebMvcTest with MockMvcTester and @MockitoBean (Java + Kotlin)
• @DataJpaTest with TestEntityManager for lazy loading verification
• Testcontainers with @ServiceConnection for PostgreSQL/Redis
• Security Testing with @WithMockUser for role-based access
• Modulith Event Testing with Scenario API

Detailed References

• Examples: See EXAMPLES.md for complete working code examples
• Troubleshooting: See TROUBLESHOOTING.md for common issues and Boot 4 migration
• Slice Tests: See references/slice-tests.md for @WebMvcTest, @DataJpaTest, @JsonTest patterns
• Testcontainers: See references/testcontainers.md for @ServiceConnection, container reuse
• Security Testing: See references/security-testing.md for @WithMockUser, JWT mocking
• Modulith Testing: See references/modulith-testing.md for Scenario API, event verification

Anti-Pattern Checklist

Anti-Pattern	Fix
Using @MockBean in Boot 4	Replace with @MockitoBean
@SpringBootTest for unit tests	Use appropriate slice annotation
Missing entityManager.clear()	Add to verify lazy loading
High-cardinality test data	Use minimal, focused fixtures
Shared mutable test state	Use @DirtiesContext or fresh containers
No security tests	Add @WithMockUser tests for endpoints

Critical Reminders

1. @MockitoBean is mandatory — @MockBean removed in Boot 4
2. Slice tests are fast — Use them for focused testing
3. Clear EntityManager — Required to test lazy loading behavior
4. @ServiceConnection simplifies Testcontainers — No more @DynamicPropertySource
5. Test security explicitly — Don't rely on disabled security