unit-test-controller-layer

Unit Test Controller Layer is a Java testing-guidance skill that provides patterns for unit testing Spring REST controllers in isolation using MockMvc and @WebMvcTest. It solves the problem of verifying the web layer — request and response mapping, input validation, HTTP status codes, headers, content negotiation, and exception handling — without spinning up the full application context or hitting real services, keeping controller tests fast and focused.

The skill lays out a clear workflow: set up standalone MockMvc around the controller, mock service dependencies with Mockito (@Mock and @InjectMocks), exercise every HTTP method (GET, POST, PUT, PATCH, DELETE) with the correct expected status codes, and assert response bodies with JsonPath. It shows how to test validation failures returning 400 with error details, error conditions returning 404/401/403/500, request and response headers including Authorization, and content negotiation. Reference documents add advanced patterns — multiple status-code scenarios, role-based access and authentication testing, file upload testing with MockMultipartFile, paginated responses, custom exception handlers, and async endpoints — along with common pitfalls and troubleshooting guidance, plus a validation loop that uses .andDo(print()) to compare actual versus expected output.

It targets Java and Spring Boot developers writing web-layer tests. Use cases include verifying REST endpoints in isolation, asserting validation and error-handling behavior, testing secured endpoints and file uploads, and generating maintainable controller test suites. It is read/write test-authoring guidance using standard testing tools, with no risky runtime behavior.