# Testing

> Testing patterns and best practices for unit, integration, and E2E testing. Use when this capability is needed.

- Skill: `tomevault-io/testing-21` (Agent Skill, multi-file: 2 files)
- Install (CLI): `npx skillmds@latest add tomevault-io/testing-21`
- Raw SKILL.md: https://api.skillmd.com/api/skills/tomevault-io/testing-21/raw
- Safety review: pending (external: skill-scanner PASS, skillspector PASS)
- Works with: Claude Code, Claude.ai, OpenAI Codex
- Category: Integrations & APIs
- Author: tomevault-io (https://skillmd.com/u/tomevault-io)
- Updated: 2026-09-17
- Page: https://skillmd.com/skills/tomevault-io/testing-21

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# 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

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