---
id: LambdaTest/agent-skills/mocha-skill
version: "c96ae94c"
license: MIT
install: manual
updated: 2026-07-24
---

# mocha-skill — mocha-skill enables you to create well-organized unit tests leveraging Mocha's hierarchical test structure and Chai's expressive assertion library. Build comprehensive test suites with clear describe blocks and individual test cases, then execute them to validate your code's behavior.

Publisher: LambdaTest · Stars: 339 · Updated: 2026-07-24

Install (manual): `git clone https://github.com/LambdaTest/agent-skills`

## SKILL.md

# Mocha Testing Skill

## Core Patterns

### Basic Test with Chai

```javascript
const { expect } = require('chai');

describe('Calculator', () => {
  let calc;
  beforeEach(() => { calc = new Calculator(); });

  it('should add two numbers', () => {
    expect(calc.add(2, 3)).to.equal(5);
  });

  it('should throw on divide by zero', () => {
    expect(() => calc.divide(10, 0)).to.throw('Division by zero');
  });
});
```

### Chai Assertions

```javascript
expect(value).to.equal(5);
expect(arr).to.have.lengthOf(3);
expect(obj).to.have.property('name');
expect(str).to.include('hello');
expect(fn).to.throw(Error);
expect(arr).to.deep.equal([1, 2, 3]);
expect(obj).to.deep.include({ name: 'Alice' });
```

### Sinon Mocking

```javascript
const sinon = require('sinon');

describe('UserService', () => {
  let sandbox;
  beforeEach(() => { sandbox = sinon.createSandbox(); });
  afterEach(() => { sandbox.restore(); });

  it('fetches user from API', async () => {
    const stub = sandbox.stub(api, 'get').resolves({ name: 'Alice' });
    const user = await userService.getUser(1);
    expect(user.name).to.equal('Alice');
    expect(stub.calledOnce).to.be.true;
  });
});
```

### Async Testing

```javascript
it('should fetch data', async () => {
  const data = await fetchData();
  expect(data).to.have.property('id');
});

it('callback style', (done) => {
  fetchData((err, data) => {
    expect(err).to.be.null;
    done();
  });
});
```

### Anti-Patterns

| Bad | Good | Why |
|-----|------|-----|
| Missing `done()` | Use async/await | Hanging tests |
| No sandbox | `sinon.createSandbox()` | Stubs leak |
| Arrow in `describe` | Regular function for `this.timeout()` | Context |

## Quick Reference

| Task | Command |
|------|---------|
| Run all | `npx mocha` |
| Watch | `npx mocha --watch` |
| Grep | `npx mocha --grep "login"` |
| Timeout | `npx mocha --timeout 10000` |
| Recursive | `npx mocha --recursive` |

## Setup: `npm install mocha chai sinon --save-dev`

## Deep Patterns → `reference/playbook.md`

| § | Section | Lines |
|---|---------|-------|
| 1 | Production Configuration | mocharc, NYC coverage, TypeScript |
| 2 | Testing with Chai + Sinon | Stubs, spies, assertions |
| 3 | Advanced Sinon Patterns | Fake timers, nock HTTP, sequential |
| 4 | Async Patterns | Promise, await, callback, events |
| 5 | Hooks & Test Organization | Lifecycle, nesting, grep tags |
| 6 | Custom Reporters & Plugins | Reporter class, root hooks |
| 7 | Express/API Testing | Supertest integration |
| 8 | CI/CD Integration | GitHub Actions, services |
| 9 | Debugging Quick-Reference | 10 common problems |
| 10 | Best Practices Checklist | 13 items |


[View on SkillFed](https://skillfed.io/LambdaTest/agent-skills/mocha-skill) · [View on GitHub](https://github.com/LambdaTest/agent-skills)