react-hooks-testing-library

Simple component wrapper and utilities for testing React hooks.

---

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 is built on top of the wonderful react-testing-library 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.

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

Example

// useTheme.js
import { useState, createContext, useContext, useMemo } from 'react'

const themes = {
  light: { primaryLight: '#FFFFFF', primaryDark: '#000000' },
  dark: { primaryLight: '#000000', primaryDark: '#FFFFFF' }
}

const ThemesContext = createContext(themes)

const useTheme = (initialTheme) => {
  const themes = useContext(ThemesContext)
  const [theme, setTheme] = useState(initialTheme)
  const toggleTheme = () => {
    setTheme(theme === 'light' ? 'dark' : 'light')
  }
  return useMemo(() => ({ ...themes[theme], toggleTheme }), [theme])
}

// useTheme.test.js
import { renderHook, cleanup, act } from 'react-hooks-testing-library'

describe('custom hook tests', () => {
  afterEach(cleanup)

  test('should use theme', () => {
    const { result } = renderHook(() => useTheme('light'))

    const theme = result.current

    expect(theme.primaryLight).toBe('#FFFFFF')
    expect(theme.primaryDark).toBe('#000000')
  })

  test('should update theme', () => {
    const { result } = renderHook(() => useTheme('light'))

    const { toggleTheme } = result.current

    act(() => toggleTheme())

    const theme = result.current

    expect(theme.primaryLight).toBe('#000000')
    expect(theme.primaryDark).toBe('#FFFFFF')
  })

  test('should use custom theme', () => {
    const customThemes = {
      light: { primaryLight: '#AABBCC', primaryDark: '#CCBBAA' },
      dark: { primaryLight: '#CCBBAA', primaryDark: '#AABBCC' }
    }

    const wrapper = ({ children }) => (
      <ThemesContext.Provider value={customThemes}>{children}</ThemesContext.Provider>
    )

    const { result } = renderHook(() => useTheme('light'), { wrapper })

    const theme = result.current

    expect(theme.primaryLight).toBe('#AABBCC')
    expect(theme.primaryDark).toBe('#CCBBAA')
  })
})

Installation

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

API

renderHook(callback[, options])

Renders a test component that will call the provided callback, including any hooks it calls, every time it renders.

Note: testHook has been renamed to renderHook. testHook will continue work in the current version with a deprecation warning, but will be removed in a future version.

You should update any usages of testHook to use renderHook instead.

Arguments

• callback (function()) - function to call each render. This function should call one or more hooks for testing.
• options (object) - accepts the same options as react-testing-library's render function, as well as:
  • initialProps (object) - the initial values to pass to the callback function

Returns

• result (object)
  • current (any) - the return value of the callback function
• rerender (function([newProps])) - function to rerender the test component including any hooks called in the callback function. If newProps are passed, the will replace the initialProps passed the the callback function for future renders.
• unmount (function()) - function to unmount the test component, commonly used to trigger cleanup effects for useEffect hooks.

cleanup()

Unmounts any React trees that were mounted with renderHook.

This is the same cleanup function that is exported by react-testing-library.

act(callback)

This is the same act function that is exported by react-testing-library.

Contributors

Thanks goes to these wonderful people (emoji key):

Michael Peyper 💻 🎨 📖 🤔 🚇 📦 ⚠️ 🔧

otofu-square 💻

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:

• Reactiflux on Discord
• Stack Overflow

LICENSE

MIT