# spring-boot-testing

> 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.

- Author: Joaquim Costa
- Repository: joaquimscosta/arkhe-claude-plugins
- Version: 20260114144030
- Stars: 4
- Forks: 0
- Last Updated: 2026-02-06
- Source: https://github.com/joaquimscosta/arkhe-claude-plugins
- Web: https://mule.run/skillshub/@@joaquimscosta/arkhe-claude-plugins~spring-boot-testing:20260114144030

---

---
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](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 |

## 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