Mock API Testing with JSON Server, Faker & JS in GitHub Actions

When building modern applications, having a fast, lightweight mock API can accelerate frontend development and test automation workflows.

In this guide, you’ll learn how to:

• Spin up a mock REST API server with json-server
• Auto-generate realistic fake data using @faker-js/faker
• Write and run API test automation in JavaScript using Mocha, Chai, and Axios
• Run the full pipeline in GitHub Actions CI 🎯

🧱 Project Structure

mock-api-server/
├── db.json
├── generate-data.js
├── routes.json
├── auth-middleware.js
├── test/
│   └── api.test.js
├── package.json

📦 package.json

Here’s a minimal but powerful package.json:

{
  "name": "mock-api-server",
  "version": "1.0.0",
  "scripts": {
    "generate": "node generate-data.js",
    "start": "npm run generate && json-server --watch db.json --routes routes.json --middlewares auth-middleware.js --port 3000",
    "test": "mocha test/*.test.js"
  },
  "devDependencies": {
    "json-server": "^0.17.3",
    "@faker-js/faker": "^8.0.2",
    "mocha": "^10.2.0",
    "chai": "^4.3.7",
    "axios": "^1.6.8"
  }
}

Key Features:

• generate: Populates db.json with fake user data
• start: Spins up a mock API server with routing and auth middleware
• test: Runs JavaScript API tests using Mocha

🔐 Add Basic Authorization Middleware

In auth-middleware.js:

module.exports = (req, res, next) => {
  const token = req.headers['authorization'];
  if (req.path.startsWith('/users') && token !== 'Bearer my-secret-token') {
    return res.status(401).json({ error: 'Unauthorized' });
  }
  next();
};

🤖 Auto-Generate Fake Data

In generate-data.js:

const fs = require('fs');
const { faker } = require('@faker-js/faker');
const generateUsers = () => {
  return Array.from({ length: 10 }, (_, id) => ({
    id: id + 1,
    name: faker.name.fullName(),
    email: faker.internet.email(),
    phone: faker.phone.number()
  }));
};
const data = {
  users: generateUsers(),
  posts: []
};
fs.writeFileSync('db.json', JSON.stringify(data, null, 2));

🧪 JavaScript Test:

test/api.test.js

const axios = require('axios');
const { expect } = require('chai');
const BASE_URL = 'http://localhost:3000';
const HEADERS = {
  Authorization: 'Bearer my-secret-token'
};
describe('Mock API Server Tests', () => {
  it('GET /users should return an array', async () => {
    const res = await axios.get(`${BASE_URL}/users`, { headers: HEADERS });
    expect(res.status).to.equal(200);
    expect(res.data).to.be.an('array');
  });
  it('POST /users should create a user', async () => {
    const res = await axios.post(`${BASE_URL}/users`, {
      name: 'Test User',
      email: 'test@example.com'
    }, { headers: HEADERS });
    expect(res.status).to.equal(201);
  });
  it('PUT /users/1 should update a user', async () => {
    const res = await axios.put(`${BASE_URL}/users/1`, {
      name: 'Updated User',
      email: 'updated@example.com'
    }, { headers: HEADERS });
    expect(res.status).to.equal(200);
  });
  it('DELETE /users/1 should delete a user', async () => {
    const res = await axios.delete(`${BASE_URL}/users/1`, { headers: HEADERS });
    expect(res.status).to.equal(200);
  });
});

🚀 GitHub Actions:

.github/workflows/test.yml

Here’s how you automate all of this in CI:

name: Mock API Server Tests
on:
  push:
    branches: [ main ]
  pull_request:
    branches: [ main ]
jobs:
  test:
    runs-on: ubuntu-latest
    steps:
      - name: Checkout code
        uses: actions/checkout@v4
      - name: Set up Node.js
        uses: actions/setup-node@v4
        with:
          node-version: '18'
      - name: Install dependencies
        run: npm install
      - name: Start mock API server in background
        run: |
          npm start &
          sleep 5  # Wait for the server to be ready
      - name: Generate Data for the tests
        run: npm run generate
      - name: Run JS API tests
        run: npm run test

🎯 Collection for all the APIs to use on Postman

### GET all users
curl --location 'http://localhost:3000/users' \
--header 'Authorization: Bearer my-secret-token'

### GET user by ID
curl --location 'http://localhost:3000/users/1' \
--header 'Authorization: Bearer my-secret-token'

### POST create new user
curl --location 'http://localhost:3000/users' \
--header 'Authorization: Bearer my-secret-token' \
--header 'Content-Type: application/json' \
--data '{
  "name": "Charlie",
  "email": "charlie@example.com"
}'

### PUT update user
curl --location --request PUT 'http://localhost:3000/users/1' \
--header 'Authorization: Bearer my-secret-token' \
--header 'Content-Type: application/json' \
--data '{
  "name": "Charlie Updated",
  "email": "charlie.updated@example.com"
}'

### DELETE user
curl --location --request DELETE 'http://localhost:3000/users/1' \
--header 'Authorization: Bearer my-secret-token'

🎯 Final Thoughts

With just a few files and no real backend, you’ve created:

• A realistic mock API server
• Fake user data using faker
• A secure endpoint with token-based auth
• Automated JavaScript tests
• CI pipeline on GitHub Actions

This setup is perfect for frontend mocks, test automation bootstraps, and sandbox environments.

I have created a project on GitHub Actions and added the code here. Also, I have added the pipeline link to view the results here.

Feel free to hit clap if you like the content. Happy Automation Testing :) Cheers. 👏

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