Mastering Jest: Day 7 — Advanced Testing Techniques with Jest

Introduction

Photo by Mohammad Rahmani on Unsplash

Welcome to the final day of our Jest journey! So far, we’ve covered the basics, snapshot testing, testing asynchronous code, and integrating Jest with Redux. Today, we’ll dive into advanced testing techniques to help you master Jest and write more efficient and reliable tests.

Mocking Modules

Mocking is essential for isolating the code under test and controlling dependencies. Jest provides powerful tools for mocking modules.

// api.js
export const fetchData = () => {
  return fetch('https://api.example.com/data')
    .then(response => response.json());
};

// api.test.js
import { fetchData } from './api';

jest.mock('./api');

test('fetchData returns data', async () => {
  const mockData = { data: 'mockData' };
  fetchData.mockResolvedValue(mockData);

  const data = await fetchData();
  expect(data).toEqual(mockData);
});

Testing Custom Hooks

Custom hooks are a vital part of React development. Testing them ensures their functionality remains intact.

// useCounter.js
import { useState } from 'react';

export const useCounter = () => {
  const [count, setCount] = useState(0);
  const increment = () => setCount(count + 1);
  const decrement = ()…