Example
Quickstart
This is a minimal setup to get you started. If you want to see a description of what each line does, scroll down to the annotated version. Scroll down to Full Example to see a more advanced test setup.
import {render, screen} from '@testing-library/react'
import userEvent from '@testing-library/user-event'
import '@testing-library/jest-dom'
import Fetch from './fetch'
test('loads and displays greeting', async () => {
// ARRANGE
render(<Fetch url="/greeting" />)
// ACT
await userEvent.click(screen.getByText('Load Greeting'))
await screen.findByRole('heading')
// ASSERT
expect(screen.getByRole('heading')).toHaveTextContent('hello there')
expect(screen.getByRole('button')).toBeDisabled()
})
Quickstart (Annotated Example)
// import react-testing methods
import {render, screen} from '@testing-library/react'
// userEvent library simulates user interactions by dispatching the events that would happen if the interaction took place in a browser.
import userEvent from '@testing-library/user-event'
// add custom jest matchers from jest-dom
import '@testing-library/jest-dom'
// the component to test
import Fetch from './fetch'
test('loads and displays greeting', async () => {
// Render a React element into the DOM
render(<Fetch url="/greeting" />)
await userEvent.click(screen.getByText('Load Greeting'))
// wait before throwing an error if it cannot find an element
await screen.findByRole('heading')
// assert that the alert message is correct using
// toHaveTextContent, a custom matcher from jest-dom.
expect(screen.getByRole('heading')).toHaveTextContent('hello there')
expect(screen.getByRole('button')).toBeDisabled()
})
Full Example
See the following sections for a detailed breakdown of the test
note
We recommend using the Mock Service Worker (MSW)
library to declaratively mock API communication in your tests instead of
stubbing window.fetch
, or relying on third-party adapters.
__tests__/fetch.test.jsx
import React from 'react'
import {http, HttpResponse} from 'msw'
import {setupServer} from 'msw/node'
import {render, fireEvent, screen} from '@testing-library/react'
import '@testing-library/jest-dom'
import Fetch from '../fetch'
const server = setupServer(
http.get('/greeting', () => {
return HttpResponse.json({greeting: 'hello there'})
}),
)
beforeAll(() => server.listen())
afterEach(() => server.resetHandlers())
afterAll(() => server.close())
test('loads and displays greeting', async () => {
render(<Fetch url="/greeting" />)
fireEvent.click(screen.getByText('Load Greeting'))
await screen.findByRole('heading')
expect(screen.getByRole('heading')).toHaveTextContent('hello there')
expect(screen.getByRole('button')).toBeDisabled()
})
test('handles server error', async () => {
server.use(
http.get('/greeting', () => {
return new HttpResponse(null, {status: 500})
}),
)
render(<Fetch url="/greeting" />)
fireEvent.click(screen.getByText('Load Greeting'))
await screen.findByRole('alert')
expect(screen.getByRole('alert')).toHaveTextContent('Oops, failed to fetch!')
expect(screen.getByRole('button')).not.toBeDisabled()
})
Step-By-Step
Imports
// import dependencies
import React from 'react'
// import API mocking utilities from Mock Service Worker
import {http, HttpResponse} from 'msw'
import {setupServer} from 'msw/node'
// import react-testing methods
import {render, fireEvent, screen} from '@testing-library/react'
// add custom jest matchers from jest-dom
import '@testing-library/jest-dom'
// the component to test
import Fetch from '../fetch'
test('loads and displays greeting', async () => {
// Arrange
// Act
// Assert
})
Mock
Use the setupServer
function from msw
to mock an API request that our tested
component makes.
// declare which API requests to mock
const server = setupServer(
// capture "GET /greeting" requests
http.get('/greeting', (req, res, ctx) => {
// respond using a mocked JSON body
return HttpResponse.json({greeting: 'hello there'})
}),
)
// establish API mocking before all tests
beforeAll(() => server.listen())
// reset any request handlers that are declared as a part of our tests
// (i.e. for testing one-time error scenarios)
afterEach(() => server.resetHandlers())
// clean up once the tests are done
afterAll(() => server.close())
// ...
test('handles server error', async () => {
server.use(
// override the initial "GET /greeting" request handler
// to return a 500 Server Error
http.get('/greeting', (req, res, ctx) => {
return new HttpResponse(null, {status: 500})
}),
)
// ...
})
Arrange
The render
method renders a React element into the DOM.
render(<Fetch url="/greeting" />)
Act
The fireEvent
method allows you to fire
events to simulate user actions.
fireEvent.click(screen.getByText('Load Greeting'))
// wait until the `get` request promise resolves and
// the component calls setState and re-renders,
// throwing an error if it cannot find an element
await screen.findByRole('heading')
Assert
// assert that the alert message is correct using
// toHaveTextContent, a custom matcher from jest-dom.
expect(screen.getByRole('alert')).toHaveTextContent('Oops, failed to fetch!')
// assert that the button is not disabled using
// toBeDisabled, a custom matcher from jest-dom.
expect(screen.getByRole('button')).not.toBeDisabled()
System Under Test
fetch.jsx
import React, {useState, useReducer} from 'react'
import axios from 'axios'
const initialState = {
error: null,
greeting: null,
}
function greetingReducer(state, action) {
switch (action.type) {
case 'SUCCESS': {
return {
error: null,
greeting: action.greeting,
}
}
case 'ERROR': {
return {
error: action.error,
greeting: null,
}
}
default: {
return state
}
}
}
export default function Fetch({url}) {
const [{error, greeting}, dispatch] = useReducer(
greetingReducer,
initialState,
)
const [buttonClicked, setButtonClicked] = useState(false)
const fetchGreeting = async url =>
axios
.get(url)
.then(response => {
const {data} = response
const {greeting} = data
dispatch({type: 'SUCCESS', greeting})
setButtonClicked(true)
})
.catch(error => {
dispatch({type: 'ERROR', error})
})
const buttonText = buttonClicked ? 'Ok' : 'Load Greeting'
return (
<div>
<button onClick={() => fetchGreeting(url)} disabled={buttonClicked}>
{buttonText}
</button>
{greeting && <h1>{greeting}</h1>}
{error && <p role="alert">Oops, failed to fetch!</p>}
</div>
)
}