Agent skill

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.

View SKILL.md on GitHub Repository
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Install this agent skill to your Project

npx add-skill https://github.com/joaquimscosta/arkhe-claude-plugins/tree/main/plugins/spring-boot/skills/spring-boot-testing

SKILL.md

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:

java
@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 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

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

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