@testing-library/react-hooks

What is @testing-library/react-hooks?

The @testing-library/react-hooks package is designed to facilitate the testing of custom React hooks. It provides a simple and complete set of utilities that work well with the React Testing Library ecosystem. With this package, you can render hooks in isolation without having to deal with components, and you can test their behavior, state changes, and side effects.

What are @testing-library/react-hooks's main functionalities?

Rendering hooks and testing their initial state

This feature allows you to render a custom hook and assert its initial state. The `renderHook` function is used to render the hook, and the `result` object is used to access the hook's return values.

import { renderHook } from '@testing-library/react-hooks';

function useCustomHook() {
  const [value, setValue] = useState(0);
  return { value, setValue };
}

test('should start with initial value', () => {
  const { result } = renderHook(() => useCustomHook());
  expect(result.current.value).toBe(0);
});

Testing hook updates

This feature allows you to test the updates of a hook's state. The `act` function is used to wrap any code that triggers updates to the hook.

import { renderHook, act } from '@testing-library/react-hooks';

function useCounter() {
  const [count, setCount] = useState(0);
  return { count, increment: () => setCount(c => c + 1) };
}

test('should increment counter', () => {
  const { result } = renderHook(() => useCounter());
  act(() => {
    result.current.increment();
  });
  expect(result.current.count).toBe(1);
});

Testing asynchronous hooks

This feature is for testing hooks that have asynchronous operations, such as data fetching. The `waitForNextUpdate` function is used to wait for the hook to update after the asynchronous operation.

import { renderHook } from '@testing-library/react-hooks';

function useFetch(url) {
  const [data, setData] = useState(null);
  useEffect(() => {
    fetch(url).then(response => response.json()).then(setData);
  }, [url]);
  return data;
}

test('should fetch data', async () => {
  const { result, waitForNextUpdate } = renderHook(() => useFetch('https://api.example.com/data'));
  await waitForNextUpdate();
  expect(result.current).not.toBeNull();
});

Other packages similar to @testing-library/react-hooks

enzyme

Enzyme is a JavaScript testing utility for React that makes it easier to assert, manipulate, and traverse your React Components' output. It does not provide a dedicated API for testing hooks in isolation, which is a key difference from @testing-library/react-hooks.

react-test-renderer

React Test Renderer is an official React package that provides a renderer that can be used to render React components to pure JavaScript objects, without depending on the DOM or a native mobile environment. It is more general-purpose compared to @testing-library/react-hooks, which is specifically tailored for testing React hooks.

README

react-hooks-testing-library

Simple and complete React hooks testing utilities that encourage good testing practices.

Read The Docs

---

The problem

You're writing an awesome custom hook and you want to test it, but as soon as you call it you see the following error:

Invariant Violation: Hooks can only be called inside the body of a function component.

You don't really want to write a component solely for testing this hook and have to work out how you were going to trigger all the various ways the hook can be updated, especially given the complexities of how you've wired the whole thing together.

The solution

The react-hooks-testing-library allows you to create a simple test harness for React hooks that handles running them within the body of a function component, as well as providing various useful utility functions for updating the inputs and retrieving the outputs of your amazing custom hook. This library aims to provide a testing experience as close as possible to natively using your hook from within a real component.

Using this library, you do not have to concern yourself with how to construct, render or interact with the react component in order to test your hook. You can just use the hook directly and assert the results.

When to use this library

1. You're writing a library with one or more custom hooks that are not directly tied to a component
2. You have a complex hook that is difficult to test through component interactions

When not to use this library

1. Your hook is defined alongside a component and is only used there
2. Your hook is easy to test by just testing the components using it

Example

useCounter.js

import { useState, useCallback } from 'react'

function useCounter() {
  const [count, setCount] = useState(0)

  const increment = useCallback(() => setCount((x) => x + 1), [])

  return { count, increment }
}

export default useCounter

useCounter.test.js

import { renderHook, act } from '@testing-library/react-hooks'
import useCounter from './useCounter'

test('should increment counter', () => {
  const { result } = renderHook(() => useCounter())

  act(() => {
    result.current.increment()
  })

  expect(result.current.count).toBe(1)
})

More advanced usage can be found in the documentation.

Installation

npm install --save-dev @testing-library/react-hooks

Peer Dependencies

react-hooks-testing-library does not come bundled with a version of react or react-test-renderer to allow you to install the specific version you want to test against. Generally, the installed versions for react and react-test-renderer should have matching versions:

npm install react@^16.9.0
npm install --save-dev react-test-renderer@^16.9.0

NOTE: The minimum supported version of react and react-test-renderer is ^16.9.0.

API

See the API reference.

Contributors

Thanks goes to these wonderful people (emoji key):

Michael Peyper 💻 🎨 📖 🤔 🚇 📦 ⚠️ 🔧	otofu-square 💻	Patrick P. Henley 🤔 👀	Matheus Marques 💻	Dhruv Patel 🐛 👀	Nathaniel Tucker 🐛 👀	Sergei Grishchenko 💻 📖 🤔
Josep M Sobrepere 📖	Marcel Tinner 📖	Daniel K. 🐛 💻	Vince Malone 💻	Sebastian Weber 📝	Christian Gill 📖	JavaScript Joe ✅
Sarah Dayan 📦	Roman Gusev 📖	Adam Seckel 💻	keiya sasaki ⚠️

This project follows the all-contributors specification. Contributions of any kind welcome!

Issues

Looking to contribute? Look for the Good First Issue label.

🐛 Bugs

Please file an issue for bugs, missing documentation, or unexpected behavior.

See Bugs

💡 Feature Requests

Please file an issue to suggest new features. Vote on feature requests by adding a 👍. This helps maintainers prioritize what to work on.

See Feature Requests

❓ Questions

For questions related to using the library, you can raise issue here, or visit a support community:

• Discord
• Stack Overflow

LICENSE

MIT