示例

快速入门

这是帮助你入门的最小示例设置。如果你想知道每一行的作用，可以滚动到 注释版。如果你想了解高级的测试配置 滚动到 完整示例。

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 () => {
  // 准备
  render(<Fetch url="/greeting" />)

  // 操作
  await userEvent.click(screen.getByText('Load Greeting'))
  await screen.findByRole('heading')

  // 断言
  expect(screen.getByRole('heading')).toHaveTextContent('hello there')
  expect(screen.getByRole('button')).toBeDisabled()
})

快速入门 (注释版)

// 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()
})

完整示例

__tests__/fetch.test.jsx

import React from 'react'
import {rest} from 'msw'
import {setupServer} from 'msw/node'
import {render, fireEvent, waitFor, screen} from '@testing-library/react'
import '@testing-library/jest-dom'
import Fetch from '../fetch'

const server = setupServer(
  rest.get('/greeting', (req, res, ctx) => {
    return res(ctx.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 waitFor(() => screen.getByRole('heading'))

  expect(screen.getByRole('heading')).toHaveTextContent('hello there')
  expect(screen.getByRole('button')).toBeDisabled()
})

test('handles server error', async () => {
  server.use(
    rest.get('/greeting', (req, res, ctx) => {
      return res(ctx.status(500))
    }),
  )

  render(<Fetch url="/greeting" />)

  fireEvent.click(screen.getByText('Load Greeting'))

  await waitFor(() => screen.getByRole('alert'))

  expect(screen.getByRole('alert')).toHaveTextContent('Oops, failed to fetch!')
  expect(screen.getByRole('button')).not.toBeDisabled()
})

我们推荐使用 Mock Service Worker 以声明方式模 拟 API 通信，而不是 stub window.fetch 方法，或是依赖第三方的适配器。

---

步骤分解

导入依赖（Imports）

// import dependencies
import React from 'react'

// import API mocking utilities from Mock Service Worker
import {rest} from 'msw'
import {setupServer} from 'msw/node'

// import react-testing methods
import {render, fireEvent, waitFor, 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 () => {
  // 准备（Arrange）
  // 调用（Act）
  // 断言（Assert）
})

模拟（Mock）

使用 msw 提供的 setupServer 函数来模拟被测试组件发起 API 请求。

// declare which API requests to mock
const server = setupServer(
  // capture "GET /greeting" requests
  rest.get('/greeting', (req, res, ctx) => {
    // respond using a mocked JSON body
    return res(ctx.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
    rest.get('/greeting', (req, res, ctx) => {
      return res(ctx.status(500))
    }),
  )

  // ...
})

准备（Arrange）

render 方法渲染一个 React 组件到 DOM。

render(<Fetch url="/greeting" />)

调用（Act）

fireEvent 方法可以让你通过派发事件来模拟 用户动作。

fireEvent.click(screen.getByText('Load Greeting'))

// wait until the `get` request promise resolves and
// the component calls setState and re-renders.
// `waitFor` waits until the callback doesn't throw an error

await waitFor(() =>
  // getByRole throws an error if it cannot find an element
  screen.getByRole('heading'),
)

断言（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()

被测试组件（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>
  )
}