Mock Generator

Generate mocks, stubs, and fakes for dependencies

Generate mocks, stubs, and fakes for external dependencies.

Instructions

1. Identify what to mock (read the function under test):

   • Database queries → mock the repository/ORM
   • HTTP calls → mock the HTTP client or use MSW
   • File I/O → mock fs module
   • Time → mock Date.now() or timers
   • Environment → mock process.env

2. Generate mocks per pattern:

// Jest manual mock — create __mocks__/database.ts
export const getUser = jest.fn();
export const saveUser = jest.fn();

// Usage in test:
jest.mock('../database');
import { getUser } from '../database';
(getUser as jest.Mock).mockResolvedValue({ id: 1, name: 'Test User' });

// MSW for HTTP mocking (intercepts at network level):
import { rest } from 'msw';
import { setupServer } from 'msw/node';

const server = setupServer(
  rest.get('/api/users/:id', (req, res, ctx) => {
    return res(ctx.json({ id: req.params.id, name: 'Mock User' }));
  })
);
beforeAll(() => server.listen());
afterEach(() => server.resetHandlers());
afterAll(() => server.close());

3. For spies (verify a function was called):

const sendEmail = jest.spyOn(emailService, 'send');
await registerUser(userData);
expect(sendEmail).toHaveBeenCalledWith(
  expect.objectContaining({ to: userData.email })
);

Rules

• Mock at the boundary (DB, HTTP, filesystem) — not internal functions
• Reset mocks between tests: beforeEach(() => jest.clearAllMocks())
• Prefer MSW over manual fetch mocks (catches real integration issues)