How can I mock dependencies in my Express.js tests?

How can I mock dependencies in my Express.js tests?

You can use libraries like Sinon or Jest to mock dependencies in your Express.js tests. Would you like a code example?

Yes, please provide a code example using Jest.

Sure! Here's a simple example:

const request = require('supertest');
const app = require('../app');
const userService = require('../services/userService');

jest.mock('../services/userService');

describe('GET /users', () => {
  it('should return a list of users', async () => {
    userService.getUsers.mockResolvedValue([{ id: 1, name: 'John Doe' }]);
    const response = await request(app).get('/users');
    expect(response.status).toBe(200);
    expect(response.body).toEqual([{ id: 1, name: 'John Doe' }]);
  });
});

This mocks the getUsers function from userService.

What if I want to test error handling?

You can mock the service to throw an error. Here's how:

userService.getUsers.mockRejectedValue(new Error('Database error'));
const response = await request(app).get('/users');
expect(response.status).toBe(500);
expect(response.body.message).toBe('Database error');