unit-test-controller-layer

# Unit Testing REST Controllers with MockMvc ## Overview Provides patterns for unit testing `@RestController` and `@Controller` classes using MockMvc. Covers request/response handling, HTTP status codes, request parameter binding, validation, content negotiation, response headers, and exception handling with mocked service dependencies. ## When to Use Use for: controller tests, API endpoint testing, Spring MVC tests, mock HTTP requests, unit testing web layer endpoints, verifying REST controllers in isolation. ## Instructions 1. **Setup standalone MockMvc**: `MockMvcBuilders.standaloneSetup(controller)` for isolated testing 2. **Mock service dependencies**: Use `@Mock` for all services, `@InjectMocks` for the controller 3. **Test HTTP methods**: GET, POST, PUT, PATCH, DELETE with correct status codes 4. **Validate responses**: JsonPath assertions for JSON, content matchers for body 5. **Test validation**: Send invalid input, verify 400 status with error details 6. **Test errors**: Verify 404, 400, 401, 403, 500 for appropriate conditions 7. **Validate headers**: Both request (Authorization) and response headers 8. **Test content negotiation**: Different Accept and Content-Type headers ### Validation Workflow ``` Run test → If fails: add .andDo(print()) → Check actual vs expected → Fix assertion ``` ## Examples ### Maven / Gradle Dependencies ```xml <dependency> <groupId>org.springframework.boot</groupId> <artifactId>spring-boot-starter-test</artifactId> <scop...