A Note about React 18 Support

As part of the changes for React 18, it has been decided that the renderHook API provided by this library will instead be included as official additions to both react-testing-library (PR) and react-native-testing-library (PR) with the intention being to provide a more cohesive and consistent implementation for our users.

Please be patient as we finalise these changes in the respective testing libraries. In the mean time you can install @testing-library/react@^13.1

Table of Contents

• The problem
• The solution
• When to use this library
• When not to use this library
• Example
  • useCounter.js
  • useCounter.test.js
• Installation
  • Peer Dependencies
• API
• Contributors
• Issues
  • 🐛 Bugs
  • 💡 Feature Requests
  • ❓ Questions
• LICENSE

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 to allow you to install the specific version you want to test against. It also does not come installed with a specific renderer, we currently support react-test-renderer and react-dom. You only need to install one of them, however, if you do have both installed, we will use react-test-renderer as the default. For more information see the installation docs. Generally, the installed versions for react and the selected 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, react-test-renderer and react-dom is ^16.9.0.

API

See the API reference.

Contributors

Thanks goes to these wonderful people (emoji key):

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