name: testing description: Testing patterns and best practices for unit, integration, and E2E testing. globs: ["/*.test.js", "/.spec.js", "**/.test.ts", "/*.spec.ts", "/test/", "/tests/", "/tests/", "/jest.config.", "**/vitest.config.", "/playwright.config.*", "/cypress.config.*"] priority: 85 tags: ["workflow"]

Testing Best Practices

Test Structure (AAA Pattern)

• Arrange: Set up test data and conditions
• Act: Execute the code under test
• Assert: Verify the expected outcome
• Use descriptive test names: "should X when Y"

Unit Tests

• Test one behavior per test
• Mock external dependencies
• Test edge cases and error paths
• Keep tests fast (< 100ms each)
• Use factories for test data
• Aim for 80%+ coverage

Integration Tests

• Test component interactions
• Use test database/containers
• Clean up after tests
• Test happy and error paths
• Use realistic data

E2E Tests

• Test critical user flows only
• Keep tests independent
• Use stable selectors (data-testid)
• Handle async properly
• Run in CI with retries

Mocking

• Mock at boundaries (APIs, DB)
• Use factories for test data
• Don't over-mock (test real behavior)
• Reset mocks between tests
• Prefer fakes over mocks when possible

Tools

• Jest/Vitest for unit tests
• Playwright/Cypress for E2E
• MSW for API mocking
• Faker for test data
• Testing Library for component tests