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
- Choose test slice → Minimal context for fast tests
- Mock dependencies →
@MockitoBean for external services
- Use Testcontainers →
@ServiceConnection for databases
- Assert thoroughly → Use AssertJ, MockMvcTester, WebTestClient
- 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
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
- @MockitoBean is mandatory —
@MockBean removed in Boot 4
- Slice tests are fast — Use them for focused testing
- Clear EntityManager — Required to test lazy loading behavior
- @ServiceConnection simplifies Testcontainers — No more
@DynamicPropertySource
- Test security explicitly — Don't rely on disabled security
