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
- Choose test slice → Minimal context for fast tests
- Mock dependencies →
@MockitoBeanfor external services - Use Testcontainers →
@ServiceConnectionfor databases - Assert thoroughly → Use AssertJ,
MockMvcTester(new),RestTestClient(new), WebTestClient - Test security →
@WithMockUser, JWT mocking
Quick Patterns
See EXAMPLES.md for complete working examples including:
- @WebMvcTest with
MockMvcTesterand@MockitoBean(Java + Kotlin) - @DataJpaTest with
TestEntityManagerfor lazy loading verification - Testcontainers with
@ServiceConnectionfor PostgreSQL/Redis - Security Testing with
@WithMockUserfor role-based access - Modulith Event Testing with
ScenarioAPI
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
- @MockitoBean is mandatory —
@MockBeanremoved 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