spring-boot-testing

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 | | MockMvc (procedural) | MockMvcTester (fluent) | New AssertJ-style API | | Implicit @AutoConfigureMockMvc | Explicit annotation required | Add to @SpringBootTest |

MockMvcTester (Spring Boot 4)

New fluent, AssertJ-style API for controller testing:

@WebMvcTest(UserController.class)
class UserControllerTest {

    @Autowired
    private MockMvcTester mvc;  // NEW: Fluent API

    @Test
    void getUser_returnsUser() {
        mvc.get().uri("/users/{id}", 1)
            .exchange()
            .assertThat()
            .hasStatusOk()
            .bodyJson()
            .extractingPath("$.name")
            .isEqualTo("John");
    }
}

Key Benefits: Fluent assertions, better error messages, AssertJ integration.

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 (new), RestTestClient (new), WebTestClient
5. Test security → @WithMockUser, JWT mocking

Quick Patterns

See [EXAMPLES.md](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](EXAMPLES.md) for complete working code examples
• Troubleshooting: See [TROUBLESHOOTING.md](TROUBLESHOOTING.md) for common issues and Boot 4 migration
• Slice Tests: See [references/SLICE-TESTS.md](references/SLICE-TESTS.md) for @WebMvcTest, @DataJpaTest, @JsonTest patterns
• Testcontainers: See [references/TESTCONTAINERS.md](references/TESTCONTAINERS.md) for @ServiceConnection, container reuse
• Security Testing: See [references/SECURITY-TESTING.md](references/SECURITY-TESTING.md) for @WithMockUser, JWT mocking
• Modulith Testing: See [references/MODULITH-TESTING.md](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 |

Related Skills

| Need | Skill | |------|-------| | Security configuration | spring-boot-security | | Module boundaries | spring-boot-modulith | | Data layer patterns | spring-boot-data-ddd | | Controller patterns | spring-boot-web-api |

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