testing▌

Unit testing REST controllers in isolation with MockMvc and mocked service dependencies. \n \n Covers testing all HTTP methods (GET, POST, PUT, PATCH, DELETE) with status code and response body validation using JsonPath assertions \n Includes patterns for request parameter binding, validation errors, exception handling, and content negotiation across different Accept and Content-Type headers \n Uses standalone MockMvc setup with Mockito to mock service layer dependencies, keeping tests focused o

Unit testing patterns for Spring @ExceptionHandler and @ControllerAdvice global exception handlers. \n \n Test exception-to-error-response transformations and HTTP status codes using MockMvc with setControllerAdvice() to register handlers \n Verify error response structure includes required fields (timestamp, status, error, message) and test field-level validation errors from MethodArgumentNotValidException \n Cover multiple exception types with appropriate status codes (404, 409, 401, 403, 500)

JUnit 5 patterns for testing utility classes, static methods, and pure functions without mocking complexity. \n \n Covers testing strategies for string manipulation, calculations, collections, data validation, and format utilities with edge case and boundary condition handling \n Uses AssertJ assertions for readable test code and @ParameterizedTest for testing multiple similar scenarios efficiently \n Emphasizes null handling, empty inputs, extreme values, and floating-point precision as critica

Unit testing JSON serialization and deserialization with Spring's @JsonTest and Jackson. \n \n Covers serialization/deserialization of POJOs, custom serializers/deserializers, field name mappings with @JsonProperty , and null handling using JacksonTester for type-safe assertions \n Includes patterns for testing nested objects, lists, date/time formatting, and polymorphic types with @JsonTypeInfo \n Provides Maven and Gradle setup, best practices for avoiding circular references and null inclusio

Structured framework for designing statistically rigorous A/B tests with mandatory validation gates. \n \n Enforces hypothesis lock, metric freezing, and sample size calculation before any implementation begins \n Includes hard gates at three critical points: hypothesis validation, assumptions review, and execution readiness \n Defines primary, secondary, and guardrail metrics to prevent harmful wins and ensure valid interpretation \n Covers test type selection, duration estimation, and strict r

Comprehensive React component testing with Jest and React Testing Library covering configuration, mocking, async patterns, and best practices. \n \n Covers Jest configuration for JavaScript and TypeScript projects, including setup files, module mapping, and coverage thresholds \n Provides query strategies prioritizing accessibility (getByRole, getByLabelText) and explains getBy, queryBy, and findBy variants \n Includes mocking patterns for modules, functions, API calls via MSW, context, and chil

Jest test patterns and best practices for NestJS unit, integration, and e2e testing. \n \n Covers the testing pyramid: unit tests for pure logic, integration tests with real providers using Test.createTestingModule , and e2e tests with supertest for HTTP APIs \n Provides patterns for mocking external services with jest.fn and test doubles, plus in-memory database adapters and test containers for data layer testing \n Emphasizes deterministic tests with proper mock reset between runs, avoiding sh

SQL and Rust testing guide covering test types, execution, and writing patterns. \n \n Three primary test formats: .sqltest (preferred for SQL compatibility across backends), TCL .test (legacy, being phased out), and Rust integration tests for regression and complex scenarios \n Run tests via make test for the full suite, make -C testing/sqltests run-cli for SQL tests, or cargo test for Rust tests \n .sqltest format uses simple declarative syntax with @database , test blocks, and expect sections

Isolated unit testing patterns for Spring service layer using Mockito and JUnit 5. \n \n Covers mocking injected dependencies, verifying service interactions, and testing business logic without database or external API calls \n Includes patterns for exception handling, complex workflows, argument capturing, and verification of call order and frequency \n Supports testing async/reactive services with CompletableFuture and provides best practices for constructor injection and spy-based partial moc

You are an expert in App Store product page optimization and A/B testing. Your goal is to help the user design, run, and interpret tests that improve their App Store conversion rate.