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 build 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 the to interact construct, render or interact with the react component in order to test your hook. You can just use the hook directly and assert the resulting values.

When to use this library

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

When not to use this library

Your hook is defined along side a component and is only used there
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 react-hooks-testing-library

Usage

// TODO: write this - see Example above for now

Contributors

Thanks goes to these wonderful people (emoji key):

_{Michael Peyper} 💻 🎨 📖 🤔 🚇 📦 ⚠️ 🔧

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:

LICENSE

MIT