Testing

We echo the guiding principles of Testing library:

• "The more your tests resemble the way your software is used, the more confidence they can give you."

We encourage you to write tests, like the user would interact with your atoms and components, therefore treating Jotai as an implementation detail.

Here's an example using React testing library:

Counter.tsx:

import { atom, useAtom } from 'jotai'

const countAtom = atom(0)

export function Counter() {
  const [count, setCount] = useAtom(countAtom)
  return (
    <h1>
      <p>{count}</p>
      <button onClick={() => setCount((c) => c + 1)}>one up</button>
    </h1>
  )
}

Counter.test.tsx:

import React from 'react'
import { render, screen } from '@testing-library/react'
import { Counter } from './Counter'

test('should increment counter', () => {
  // Arrange
  render(<Counter />)

  const counter = screen.getByText('0')
  const incrementButton = screen.getByText('one up')
  // Act
  fireEvent.click(incrementButton)
  // Assert
  expect(counter.textContent).toEqual('1')
})

Custom hooks

If you have complex atoms, sometimes you want to test them in isolation.

For that, you can use React Hooks Testing Library. Here's an example below:

countAtom.ts:

import { useAtom } from 'jotai'
import { atomWithReducer } from 'jotai/utils'

const reducer = (state: number, action?: 'INCREASE' | 'DECREASE') => {
  switch (action) {
    case 'INCREASE':
      return state + 1
    case 'DECREASE':
      return state - 1
    case undefined:
      return state
  }
}
export const countAtom = atomWithReducer(0, reducer)

countAtom.test.ts:

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

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

  act(() => {
    result.current[1]('INCREASE')
  })

  expect(result.current[0]).toBe(1)
})