---
name: mocha-skill
description: >
  Generates Mocha tests in JavaScript with Chai assertions and Sinon mocking.
  Use when user mentions "Mocha", "Chai", "sinon", "describe/it (not Jest)".
  Triggers on: "Mocha", "Chai", "sinon", "mocha test".
languages:
  - JavaScript
  - TypeScript
category: unit-testing
license: MIT
metadata:
  author: TestMu AI
  version: "1.0"
---

# 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 |

## Source and license

Source: https://github.com/LambdaTest/agent-skills/blob/0491a3a29aa18558d2c3c64ff09367adb976c56f/mocha-skill/SKILL.md

MIT License

Copyright (c) 2025 TestMu AI / LambdaTest

Permission is hereby granted, free of charge, to any person obtaining a copy
of this software and associated documentation files (the "Software"), to deal
in the Software without restriction, including without limitation the rights
to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
copies of the Software, and to permit persons to whom the Software is
furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in all
copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
SOFTWARE.