Mocha Testing Skill
Core Patterns
Basic Test with Chai
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
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
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
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 |
