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 Scan Documentation: Check .agent/SYSTEM/ARCHITECTURE.md for testing architecture Identify Tools: Jest/Vitest, React Testing Library, Supertest, Playwright/Cypress Discover Patterns: Review existing test files, utilities, mocking patterns 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) 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 Test Isolation: Each test independent, clean up after Meaningful Tests: Test behavior, not implementation Mocking Strategy: Mock external dependencies, not what you're testing Test Data: Use factories, keep data minimal, clean up 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