react测试组件

The easiest way to start with testing React components is doing snapshot testing, a testing technique that lets you test components in isolation.

开始测试React组件的最简单方法是进行快照测试，这是一种测试技术，可让您隔离测试组件。

If you are familiar with testing software, it’s just like unit testing you do for classes: you test each component functionality.

如果您熟悉测试软件，就像您对类进行单元测试一样：您测试每个组件的功能。

I assume you created a React app with create-react-app, which already comes with Jest installed, the testing package we’ll need.

我假设您使用create-react-app创建了一个React应用，该create-react-app已经安装了Jest ，这是我们需要的测试包。

Let’s start with a simple test. CodeSandbox is a great environment to try this out. Start with a React sandbox, and create an App.js component in a components folder, and add an App.test.js file.

让我们从一个简单的测试开始。 CodeSandbox是一个很好的尝试环境。 从React沙箱开始，在components文件夹中创建一个App.js组件，然后添加一个App.test.js文件。

import React from 'react'export default function App() {  return (    
     
      
      
Hello CodeSandbox
      
      
Start editing to see some magic happen!
    
     
  )}

Our first test is dumb:

我们的第一个测试是愚蠢的：

test('First test', () => {  expect(true).toBeTruthy()})

When CodeSandbox detects test files, it automatically runs them for you, and you can click the Tests button in the bottom of the view to show your test results:

当CodeSandbox检测到测试文件时，它将自动为您运行它们，您可以单击视图底部的“测试”按钮以显示测试结果：

A test file can contain multiple tests:

一个测试文件可以包含多个测试：

Let’s do something a bit more useful now, to actually test a React component. We only have App now, which is not doing anything really useful, so let’s first set up the environment with a little application with more functionality: the counter app we built previously. If you skipped it, you can go back and read how we built it, but for easier reference I add it here again.

现在让我们做一些更有用的操作，以实际测试React组件。 现在我们只有App，它并没有做任何真正有用的事情，因此让我们首先使用一个具有更多功能的小应用程序来设置环境：我们之前构建的计数器应用程序。 如果您跳过它，则可以返回并阅读我们如何构建它，但是为了便于参考，我再次在此处添加它。

It’s just 2 components: App and Button. Create the App.js file:

它只有2个组件：App和Button。 创建App.js文件：

import React, { useState } from 'react'import Button from './Button'const App = () => {  const [count, setCount] = useState(0)  const incrementCount = increment => {    setCount(count + increment)  }  return (    
     
      
            
            
            
            
      {count}    
     
  )}export default App

and the Button.js file:

和Button.js文件：

import React from 'react'const Button = ({ increment, onClickFunction }) => {  const handleClick = () => {    onClickFunction(increment)  }  return +{increment}}export default Button

We are going to use the react-testing-library, which is a great help as it allows us to inspect the output of every component and to apply events on them. You can read more about it on or by watching .

我们将使用react-testing-library ，这是一个很大的帮助，因为它允许我们检查每个组件的输出并将事件应用于它们。 您可以在或观看了解更多信息。

Let’s test the Button component first.

让我们首先测试Button组件。

We start by importing render and fireEvent from react-testing-library, two helpers. The first lets us render JSX. The second lets us emit events on a component.

我们从两个帮助程序react-testing-library导入render和fireEvent开始。 第一个让我们渲染JSX。 第二个让我们在组件上发出事件。

Create a Button.test.js and put it in the same folder as Button.js.

创建一个Button.test.js并将其放在与Button.js相同的文件夹中。

import React from 'react'import { render, fireEvent } from 'react-testing-library'import Button from './Button'

Buttons are used in the app to accept a click event and then they call a function passed to the onClickFunction prop. We add a count variable and we create a function that increments it:

应用程序中使用按钮来接受click事件，然后它们调用传递给onClickFunction的函数。 我们添加一个count变量，并创建一个递增它的函数：

let countconst incrementCount = increment => {  count += increment}

Now off to the actual tests. We first initialize count to 0, and we render a +1 Button component passing a 1 to increment and our incrementCount function to onClickFunction.

现在开始实际测试。 我们首先初始化计数为0，我们呈现一个+1 Button组件传递一个1到increment和我们incrementCount功能onClickFunction 。

Then we get the content of the first child of the component, and we check it outputs +1.

然后，我们获得组件第一个子代的内容，并检查其输出+1 。

We then proceed to clicking the button, and we check that the count got from 0 to 1:

然后，我们继续单击按钮，并检查计数是否从0变为1：

test('+1 Button works', () => {  count = 0  const { container } = render(      )  const button = container.firstChild  expect(button.textContent).toBe('+1')  expect(count).toBe(0)  fireEvent.click(button)  expect(count).toBe(1)})

Similarly we test a +100 button, this time checking the output is +100 and the button click increments the count of 100.

同样，我们测试了一个+100按钮，这次检查输出为+100并且单击按钮将计数增加100。

test('+100 Button works', () => {  count = 0  const { container } = render(      )  const button = container.firstChild  expect(button.textContent).toBe('+100')  expect(count).toBe(0)  fireEvent.click(button)  expect(count).toBe(100)})

Let’s test the App component now. It shows 4 buttons and the result in the page. We can inspect each button and see if the result increases when we click them, clicking multiple times as well:

现在让我们测试App组件。 它在页面中显示4个按钮和结果。 我们可以检查每个按钮，并在单击它们时也多次单击以查看结果是否增加：

import React from 'react'import { render, fireEvent } from 'react-testing-library'import App from './App'test('App works', () => {  const { container } = render(
     )  console.log(container)  const buttons = container.querySelectorAll('button')  expect(buttons[0].textContent).toBe('+1')  expect(buttons[1].textContent).toBe('+10')  expect(buttons[2].textContent).toBe('+100')  expect(buttons[3].textContent).toBe('+1000')  const result = container.querySelector('span')  expect(result.textContent).toBe('0')  fireEvent.click(buttons[0])  expect(result.textContent).toBe('1')  fireEvent.click(buttons[1])  expect(result.textContent).toBe('11')  fireEvent.click(buttons[2])  expect(result.textContent).toBe('111')  fireEvent.click(buttons[3])  expect(result.textContent).toBe('1111')  fireEvent.click(buttons[2])  expect(result.textContent).toBe('1211')  fireEvent.click(buttons[1])  expect(result.textContent).toBe('1221')  fireEvent.click(buttons[0])  expect(result.textContent).toBe('1222')})

Check the code working on this CodeSandbox:

检查在此CodeSandbox上运行的代码： ://codesandbox.io/s/pprl4y0wq

翻译自:

react测试组件