testing-expert

# Testing Expert Skill Expert in testing strategies for React, Next.js, and NestJS applications. ## When to Use This Skill - Writing unit tests - Creating integration tests - Setting up E2E tests - Testing React components - Testing API endpoints - Testing database operations - Setting up test infrastructure - Reviewing test coverage ## Project Context Discovery 1. **Scan Documentation:** Check `.agents/SYSTEM/ARCHITECTURE.md` for testing architecture 2. **Identify Tools:** Jest/Vitest, React Testing Library, Supertest, Playwright/Cypress 3. **Discover Patterns:** Review existing test files, utilities, mocking patterns 4. **Use Project-Specific Skills:** Check for `[project]-testing-expert` skill ## Core Testing Principles ### Testing Pyramid - **Unit Tests** (70%): Fast, isolated, test individual functions/components - **Integration Tests** (20%): Test component interactions - **E2E Tests** (10%): Test full user flows ### Coverage Targets - Line coverage: > 80% - Branch coverage: > 75% - Function coverage: > 85% - Critical paths: 100% ### Test Organization ``` src/ users/ users.controller.ts users.controller.spec.ts # Unit tests users.service.ts users.service.spec.ts __tests__/ integration/ e2e/ ``` ### Test Quality (AAA Pattern) ```typescript it('should return users filtered by organization', async () => { // Arrange: Set up test data const organizationId = 'org1'; const expectedUsers = [{ organization: organizationId }]; // Act: Execute the code being tested const result = await service.findAll(organizationId); // Assert: Verify the result expect(result).toEqual(expectedUsers); }); ``` ## Good Tests Are - Independent (no test dependencies) - Fast (< 100ms each) - Repeatable (same result every time) - Meaningful (test real behavior) - Maintainable (easy to update) ## Testing Best Practices Summary 1. **Test Isolation:** Each test independent, clean up after 2. **Meaningful Tests:** Test behavior, not implementation 3. **Mocking Strategy:** Mock external dependencies, not what you're testing 4. **Test Data:** Use factories, keep data minimal, clean up 5. **Coverage:** High coverage, focus on critical paths ## Integration | Test Type | Tools | Use Case | |-----------|-------|----------| | Unit | Jest/Vitest | Functions, components, services | | Integration | Supertest + Jest | Controller + Service + DB | | E2E | Playwright/Cypress | Full user flows | | Component | React Testing Library | React component behavior | --- **For complete React Testing Library examples, hook testing, Next.js page/API testing, NestJS service/controller testing, integration test setup, E2E test patterns, MongoDB testing, authentication helpers, test fixtures, and mocking patterns, see:** `references/full-guide.md`