mock-server

Mock Server Skill

Create and manage mock API servers for development and testing.

Instructions

You are a mock API server expert. When invoked:

1. Create Mock Servers:
2. Generate mock API endpoints from OpenAPI specs
3. Create custom mock responses
4. Simulate different response scenarios
5. Mock REST and GraphQL APIs
6. Handle various HTTP methods

1. Configure Behavior:
2. Set response delays/latency
3. Simulate error conditions
4. Return different responses based on input
5. Implement state management
6. Mock authentication

1. Advanced Scenarios:
2. Simulate network failures
3. Random error injection
4. Rate limiting simulation
5. Conditional responses
6. CORS configuration

1. Integration:
2. Proxy to real APIs
3. Record and replay requests
4. Generate mock data
5. Integration with testing frameworks

Usage Examples

@mock-server
@mock-server --from-openapi
@mock-server --port 3000
@mock-server --with-delays
@mock-server --graphql

JSON Server (Simple Mock)

Quick Setup

# Install
npm install -g json-server

# Create db.json
cat > db.json << EOF
{
  "users": [
    { "id": 1, "name": "John Doe", "email": "john@example.com" },
    { "id": 2, "name": "Jane Smith", "email": "jane@example.com" }
  ],
  "posts": [
    { "id": 1, "title": "Hello World", "userId": 1 },
    { "id": 2, "title": "Mock APIs", "userId": 2 }
  ]
}
EOF

# Start server
json-server --watch db.json --port 3000

Available Endpoints (Auto-generated)

# GET all users
curl http://localhost:3000/users

# GET user by ID
curl http://localhost:3000/users/1

# POST new user
curl -X POST http://localhost:3000/users \
  -H "Content-Type: application/json" \
  -d '{"name": "Bob", "email": "bob@example.com"}'

# PUT update user
curl -X PUT http://localhost:3000/users/1 \
  -H "Content-Type: application/json" \
  -d '{"id": 1, "name": "John Updated", "email": "john.new@example.com"}'

# PATCH partial update
curl -X PATCH http://localhost:3000/users/1 \
  -H "Content-Type: application/json" \
  -d '{"name": "John Patched"}'

# DELETE user
curl -X DELETE http://localhost:3000/users/1

# Query parameters
curl "http://localhost:3000/users?_page=1&_limit=10"
curl "http://localhost:3000/users?_sort=name&_order=asc"
curl "http://localhost:3000/posts?userId=1"

Custom Routes

// routes.json
{
  "/api/*": "/$1",
  "/users/:id/posts": "/posts?userId=:id",
  "/auth/login": "/login"
}

// Start with custom routes
json-server db.json --routes routes.json

Mock Service Worker (MSW)

Setup

npm install --save-dev msw

REST API Mocking

// src/mocks/handlers.js
import { http, HttpResponse } from 'msw';

export const handlers = [
  // GET users
  http.get('/api/users', () => {
    return HttpResponse.json([
      { id: '1', name: 'John Doe', email: 'john@example.com' },
      { id: '2', name: 'Jane Smith', email: 'jane@example.com' }
    ]);
  }),

  // GET user by ID
  http.get('/api/users/:userId', ({ params }) => {
    const { userId } = params;

    // Simulate not found
    if (userId === '999') {
      return new HttpResponse(null, { status: 404 });
    }

    return HttpResponse.json({
      id: userId,
      name: 'John Doe',
      email: 'john@example.com'
    });
  }),

  // POST create user
  http.post('/api/users', async ({ request }) => {
    const data = await request.json();

    // Simulate validation error
    if (!data.email) {
      return HttpResponse.json(
        { error: 'Email is required' },
        { status: 400 }
      );
    }

    return HttpResponse.json(
      {
        id: '123',
        ...data,
        createdAt: new Date().toISOString()
      },
      { status: 201 }
    );
  }),

  // PUT update user
  http.put('/api/users/:userId', async ({ params, request }) => {
    const { userId } = params;
    const data = await request.json();

    return HttpResponse.json({
      id: userId,
      ...data,
      updatedAt: new Date().toISOString()
    });
  }),

  // DELETE user
  http.delete('/api/users/:userId', ({ params }) => {
    return new HttpResponse(null, { status: 204 });
  }),

  // Simulate delay
  http.get('/api/slow-endpoint', async () => {
    await delay(2000); // 2 second delay
    return HttpResponse.json({ message: 'Slow response' });
  }),

  // Simulate random errors
  http.get('/api/unreliable', () => {
    if (Math.random() > 0.5) {
      return new HttpResponse(null, { status: 500 });
    }
    return HttpResponse.json({ status: 'ok' });
  }),

  // Authentication
  http.post('/api/auth/login', async ({ request }) => {
    const { email, password } = await request.json();

    if (email === 'user@example.com' && password === 'password') {
      return HttpResponse.json({
        accessToken: 'mock-jwt-token',
        refreshToken: 'mock-refresh-token',
        expiresIn: 3600
      });
    }

    return HttpResponse.json(
      { error: 'Invalid credentials' },
      { status: 401 }
    );
  })
];

function delay(ms) {
  return new Promise(resolve => setTimeout(resolve, ms));
}

Browser Setup

// src/mocks/browser.js
import { setupWorker } from 'msw/browser';
import { handlers } from './handlers';

export const worker = setupWorker(...handlers);

// src/index.js
if (process.env.NODE_ENV === 'development') {
  const { worker } = await import('./mocks/browser');
  await worker.start();
}

Node.js Setup (Testing)

// src/mocks/server.js
import { setupServer } from 'msw/node';
import { handlers } from './handlers';

export const server = setupServer(...handlers);

// src/tests/setup.js
import { server } from '../mocks/server';

beforeAll(() => server.listen());
afterEach(() => server.resetHandlers());
afterAll(() => server.close());

Prism (OpenAPI-based)

From OpenAPI Spec

# Install
npm install -g @stoplight/prism-cli

# Start mock server from OpenAPI spec
prism mock openapi.yaml

# Specify port
prism mock openapi.yaml --port 4010

# Enable validation
prism mock openapi.yaml --errors

# Dynamic responses based on examples
prism mock openapi.yaml --dynamic

Example OpenAPI for Prism

openapi: 3.0.0
info:
  title: Mock API
  version: 1.0.0

paths:
  /api/users:
    get:
      responses:
        '200':
          description: Success
          content:
            application/json:
              schema:
                type: array
                items:
                  $ref: '#/components/schemas/User'
              examples:
                success:
                  value:
                    - id: "1"
                      name: "John Doe"
                      email: "john@example.com"

  /api/users/{userId}:
    get:
      parameters:
        - name: userId
          in: path
          required: true
          schema:
            type: string
      responses:
        '200':
          description: Success
          content:
            application/json:
              schema:
                $ref: '#/components/schemas/User'
              examples:
                user:
                  value:
                    id: "1"
                    name: "John Doe"
                    email: "john@example.com"
        '404':
          description: Not found
          content:
            application/json:
              examples:
                notFound:
                  value:
                    error: "User not found"

components:
  schemas:
    User:
      type: object
      properties:
        id:
          type: string
        name:
          type: string
        email:
          type: string

Express Mock Server

Custom Implementation

const express = require('express');
const cors = require('cors');

const app = express();

app.use(cors());
app.use(express.json());

// Middleware for random delays
app.use((req, res, next) => {
  const delay = Math.random() * 1000; // 0-1 second
  setTimeout(next, de