tdd-patterns

name	tdd-patterns
description	TDD workflow, per-layer test types, naming conventions, and test fixture patterns for Spring Boot. Use when writing or reviewing tests.
triggers	["tdd","test first","red green refactor","@test","junit5","mockito mock","testcontainers","단위 테스트","통합 테스트"]

Note: The tdd keyword may also trigger OMX/Codex's built-in TDD guidance. This overlap is acceptable — the built-in guidance provides general TDD workflow while this skill provides project-specific layer test patterns and fixture conventions.

1. TDD Workflow

• RED: Write failing test FIRST (compile error is OK)
• GREEN: Write minimum code to pass
• REFACTOR: Clean up, extract, rename
• Repeat for next behavior

2. Test Types by Layer

Layer	Test Type	Framework	What to Test	What to Mock
Entity/Domain	Unit	JUnit 5	Invariants, validation, state transitions, equality	Nothing
Domain Service	Unit	JUnit 5 + Mockito	Business logic, cross-aggregate rules	Repository interfaces
Application Service	Unit	JUnit 5 + Mockito	Orchestration, DTO conversion, event publishing	Repository, domain services, infra
Application Service	Integration	@SpringBootTest + Testcontainers	Full flow with real DB	External APIs only
Controller	Slice	@WebMvcTest	Request mapping, validation, serialization	Application service
Repository	Slice	@DataJpaTest + Testcontainers	Custom queries, projections	Nothing

3. Test Naming Convention

Pattern: should_{expected_behavior}_when_{condition}

Example
should_create_order_when_valid_request
should_throw_exception_when_insufficient_stock
should_return_empty_when_product_not_found
should_publish_event_when_order_placed

4. Test Fixture Patterns

Pattern	When	How
Builder/Factory	Domain objects	OrderFixture.aValidOrder().withStatus(PENDING).build()
@Sql	DB state setup	@Sql("/test-data/orders.sql")
Testcontainers	Integration tests needing Kafka/PostgreSQL/ES	@Container static PostgreSQLContainer<?>
@MockBean	Spring slice tests	Mock application service in controller test
ArgumentCaptor	Verify event publishing	ArgumentCaptor<OrderCreatedEvent>

5. Test Organization

• Test class mirrors source class: OrderService -> OrderServiceTest
• src/test/java mirrors src/main/java package structure
• Integration tests annotated @Tag("integration")
• Unit tests run in < 1 second each
• @Nested for grouping related scenarios