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