Test Node.js applications with Jest including unit tests, integration tests, mocking, code coverage, and CI/CD integration
Write and run Jest tests for Node.js applications, including unit/integration tests, mocking, and code coverage. Use when you need to test JavaScript code or verify API endpoints.
/plugin marketplace add pluginagentmarketplace/custom-plugin-nodejs/plugin install nodejs-developer-plugin@pluginagentmarketplace-nodejsThis skill inherits all available tools. When active, it can use any tool Claude has access to.
assets/config.yamlreferences/GUIDE.mdscripts/helper.pyMaster testing Node.js applications with Jest - the delightful JavaScript testing framework.
Test in 3 steps:
npm install --save-dev jest supertest*.test.js filesnpm test// sum.test.js
const sum = require('./sum');
describe('sum function', () => {
test('adds 1 + 2 to equal 3', () => {
expect(sum(1, 2)).toBe(3);
});
test('adds negative numbers', () => {
expect(sum(-1, -2)).toBe(-3);
});
});
// package.json
{
"scripts": {
"test": "jest",
"test:watch": "jest --watch",
"test:coverage": "jest --coverage"
},
"jest": {
"testEnvironment": "node",
"coverageThreshold": {
"global": {
"branches": 80,
"functions": 80,
"lines": 80
}
}
}
}
// userService.test.js
const UserService = require('./userService');
const User = require('./models/User');
jest.mock('./models/User');
describe('UserService', () => {
beforeEach(() => {
jest.clearAllMocks();
});
describe('createUser', () => {
it('should create user successfully', async () => {
const userData = {
name: 'John',
email: 'john@example.com'
};
User.create.mockResolvedValue({ id: 1, ...userData });
const result = await UserService.createUser(userData);
expect(User.create).toHaveBeenCalledWith(userData);
expect(result.id).toBe(1);
});
it('should throw error for duplicate email', async () => {
User.create.mockRejectedValue(new Error('Email exists'));
await expect(UserService.createUser({}))
.rejects
.toThrow('Email exists');
});
});
});
const request = require('supertest');
const app = require('./app');
describe('User API', () => {
describe('POST /api/users', () => {
it('should create new user', async () => {
const userData = {
name: 'John',
email: 'john@example.com',
password: 'password123'
};
const response = await request(app)
.post('/api/users')
.send(userData)
.expect('Content-Type', /json/)
.expect(201);
expect(response.body).toHaveProperty('id');
expect(response.body.email).toBe(userData.email);
});
it('should return 400 for invalid email', async () => {
const response = await request(app)
.post('/api/users')
.send({ email: 'invalid' })
.expect(400);
expect(response.body).toHaveProperty('error');
});
});
describe('GET /api/users/:id', () => {
it('should return user by id', async () => {
const response = await request(app)
.get('/api/users/123')
.expect(200);
expect(response.body.id).toBe('123');
});
it('should return 404 for non-existent user', async () => {
await request(app)
.get('/api/users/999')
.expect(404);
});
});
});
// Mock entire module
jest.mock('axios');
const axios = require('axios');
test('fetches data from API', async () => {
axios.get.mockResolvedValue({ data: { id: 1 } });
const result = await fetchUser(1);
expect(axios.get).toHaveBeenCalledWith('/api/users/1');
expect(result.id).toBe(1);
});
// Spy on function
test('calls callback', () => {
const callback = jest.fn();
processData('test', callback);
expect(callback).toHaveBeenCalledWith('test');
expect(callback).toHaveBeenCalledTimes(1);
});
// Mock timers
jest.useFakeTimers();
test('delays execution', () => {
const callback = jest.fn();
setTimeout(callback, 1000);
jest.advanceTimersByTime(1000);
expect(callback).toHaveBeenCalled();
});
describe('User Tests', () => {
beforeAll(async () => {
// Setup test database
await connectTestDB();
});
afterAll(async () => {
// Cleanup
await disconnectTestDB();
});
beforeEach(async () => {
// Clear data before each test
await User.deleteMany({});
});
afterEach(() => {
// Cleanup after each test
jest.clearAllMocks();
});
test('...', () => {});
});
// Equality
expect(value).toBe(expected) // Strict equality (===)
expect(value).toEqual(expected) // Deep equality
expect(value).not.toBe(expected) // Negation
// Truthiness
expect(value).toBeDefined()
expect(value).toBeNull()
expect(value).toBeTruthy()
expect(value).toBeFalsy()
// Numbers
expect(value).toBeGreaterThan(3)
expect(value).toBeGreaterThanOrEqual(3)
expect(value).toBeLessThan(5)
expect(value).toBeCloseTo(0.3) // Floating point
// Strings
expect(string).toMatch(/pattern/)
expect(string).toContain('substring')
// Arrays
expect(array).toContain(item)
expect(array).toHaveLength(3)
// Objects
expect(obj).toHaveProperty('key')
expect(obj).toMatchObject({ key: 'value' })
// Exceptions
expect(() => fn()).toThrow()
expect(() => fn()).toThrow('error message')
// Async
await expect(promise).resolves.toBe(value)
await expect(promise).rejects.toThrow()
# Run with coverage
npm test -- --coverage
# Coverage report shows:
# - Statements: % of code executed
# - Branches: % of if/else paths
# - Functions: % of functions called
# - Lines: % of lines executed
# .github/workflows/test.yml
name: Tests
on: [push, pull_request]
jobs:
test:
runs-on: ubuntu-latest
steps:
- uses: actions/checkout@v3
- uses: actions/setup-node@v3
with:
node-version: 18
- run: npm ci
- run: npm test -- --coverage
- uses: codecov/codecov-action@v3
Use Jest testing when:
This skill should be used when the user asks to "create a slash command", "add a command", "write a custom command", "define command arguments", "use command frontmatter", "organize commands", "create command with file references", "interactive command", "use AskUserQuestion in command", or needs guidance on slash command structure, YAML frontmatter fields, dynamic arguments, bash execution in commands, user interaction patterns, or command development best practices for Claude Code.
This skill should be used when the user asks to "create an agent", "add an agent", "write a subagent", "agent frontmatter", "when to use description", "agent examples", "agent tools", "agent colors", "autonomous agent", or needs guidance on agent structure, system prompts, triggering conditions, or agent development best practices for Claude Code plugins.
This skill should be used when the user asks to "create a hook", "add a PreToolUse/PostToolUse/Stop hook", "validate tool use", "implement prompt-based hooks", "use ${CLAUDE_PLUGIN_ROOT}", "set up event-driven automation", "block dangerous commands", or mentions hook events (PreToolUse, PostToolUse, Stop, SubagentStop, SessionStart, SessionEnd, UserPromptSubmit, PreCompact, Notification). Provides comprehensive guidance for creating and implementing Claude Code plugin hooks with focus on advanced prompt-based hooks API.