Mocking API calls with Jest

mocking-api-calls-with-jest.js

// api.test.js
const axios = require('axios');
const fetchData = require('../api');

// Mock the axios module
jest.mock('axios');

describe('API Call Tests', () => {
  
  // Reset all mocks before each test to ensure test isolation
  beforeEach(() => {
    jest.clearAllMocks();
  });

  it('fetches successfully data from an API', async () => {
    const data = { name: 'John Doe' };

    // Mocking the resolved value of axios.get
    axios.get.mockResolvedValue({ data });

    const result = await fetchData('https://example.com/user');
    expect(result).toEqual(data);
    expect(axios.get).toHaveBeenCalledWith('https://example.com/user');
  });

  it('handles API error correctly', async () => {
    const errorMessage = 'Network Error';

    // Mocking the rejected value of axios.get
    axios.get.mockRejectedValue(new Error(errorMessage));

    await expect(fetchData('https://example.com/user')).rejects.toThrow(errorMessage);
    expect(axios.get).toHaveBeenCalledWith('https://example.com/user');
  });
});