# Jest

> Writes unit and integration tests with Jest, including mocks, snapshots, and code coverage. Use for JavaScript/TypeScript testing.

- Skill: `ssrjkk/jest` (Agent Skill, multi-file: 2 files)
- Install (CLI): `npx skillmds@latest add ssrjkk/jest`
- Raw SKILL.md: https://api.skillmd.com/api/skills/ssrjkk/jest/raw
- Safety review: pending (external: skill-scanner PASS, skillspector PASS)
- Works with: Claude Code, Claude.ai, OpenAI Codex
- Category: Integrations & APIs
- Author: ssrjkk (https://skillmd.com/u/ssrjkk)
- Updated: 2026-08-19
- Page: https://skillmd.com/skills/ssrjkk/jest

---

# Jest

> Delightful JavaScript testing with built-in mocking and assertions.

## Quick Start
```javascript
// sum.test.js
const sum = (a, b) => a + b;

test('adds 1 + 2 to equal 3', () => {
  expect(sum(1, 2)).toBe(3);
});
```

## When to Use
- Unit and integration tests
- React component testing
- API endpoint testing
- Snapshot testing

## Step-by-Step
1. Install: `npm install --save-dev jest`
2. Add `"test": "jest"` to package.json
3. Write tests in `*.test.js` files
4. Run: `npm test`

## Dependencies
```bash
npm install --save-dev jest @types/jest ts-jest
```

## Examples
```javascript
import axios from 'axios';
jest.mock('axios');

test('fetches users', async () => {
  axios.get.mockResolvedValue({ data: [{ id: 1 }] });
  const users = await fetchUsers();
  expect(users).toHaveLength(1);
});
```

## Resources
- [Jest Docs](https://jestjs.io/docs/getting-started)

## Validation
1. Tests pass with `npm test`
2. Coverage report generates
3. Mocks work correctly