如何在react使用jest

第一步，我们需要安装所需依赖包进行支持：

npm install @babel/plugin-transform-react-jsx @testing-library/jest-dom @testing-library/react jest --save-dev

第二步，我们需要在babel.config.js中加入jsx转换：

module.exports = {
    
    
	presets: [['babel-preset-env', {
    
     targets: {
    
     node: 'current' } }]],
	++ 'plugins': ['@babel/plugin-transform-react-jsx'] // 需要加入的配置
}

第三步，我们需要新建jest.config.js来配置jest：

// 根目录下创建： jest.config.js

// 配置文档
//https://jestjs.io/docs/zh-Hans/configuration
module.exports = {
    
    
	// Automatically clear mock calls and instances between every test
	clearMocks: true,
	// The directory where Jest should output its coverage files
	coverageDirectory: 'coverage',
	// An array of regexp pattern strings used to skip coverage collection
	coveragePathIgnorePatterns: [
		'\\\\node_modules\\\\'
	],
	// An array of file extensions your modules use
	moduleFileExtensions: [
		'js',
		'jsx',
	],
	// A list of paths to directories that Jest should use to search for files in
	roots: null,
	// The test environment that will be used for testing
	// testEnvironment: 'node',
	testEnvironment: 'jsdom',
	// The glob patterns Jest uses to detect test files
	testMatch: [
		'**/__tests__/**/*.js?(x)',
		//"**/?(*.)+(spec|test).js?(x)"
	],
	// An array of regexp pattern strings that are matched against all test paths, matched tests are skipped
	testPathIgnorePatterns: [
		'\\\\node_modules\\\\'
	],
	// A map from regular expressions to paths to transformers
	transform: {
    
    
		'^.+\\.js$': 'babel-jest',
	},
	// An array of regexp pattern strings that are matched against all source file paths, matched files will skip transformation
	transformIgnorePatterns: [
		'\\\\node_modules\\\\'
	],
	// moduleNameMapper: {
    
    
	// 	'\\.(css|less)$': 'identify-obj-proxy'
	// }
}

单元测试文件统一放在src/__tests__目录下，如果需要修改，请修改jest.config.js中的testMatch下的规则

但是我们一般会在jsx中引入了css或less样式，所以为了jest支持less，我们还需要额外增加配置来支持less。

我们需要安装jest-less-loader来让jest识别less：

npm install jest-less-loader --save-dev

然后在jest.config.js中增加以下配置：

module.exports = {
    
    
	...
	transform: {
    
    
		'^.+\\.js$': 'babel-jest',
		++ '\\.(less|css)$': 'jest-less-loader' // 支持less
	},
	...
}

这个时候运行jest进行单元测试就可以了。

案例：
src/__tests__/tab-test.js

import React from 'react'
import ReactDOM from 'react-dom'
import TestUtils from 'react-dom/test-utils'
import Tabs from '../components/Tab/Tabs.js'
import TabPane from '../components/Tab/TabPane'

describe('tab', ()=>{
    
    
	it('render the tab content', function () {
    
    
		const tab = TestUtils.renderIntoDocument(
			<Tabs classPrefix={
    
    'tabs'} defaultActiveIndex={
    
    0} className="ui-tabs">
				<TabPane order={
    
    0} tab={
    
    'Tab 1'}>第一个Tab里的内容</TabPane>
				<TabPane order={
    
    1} tab={
    
    'Tab 2'}>第二个Tab里的内容</TabPane>
				<TabPane order={
    
    2} tab={
    
    'Tab 3'}>第三个Tab里的内容</TabPane>
			</Tabs>
		)
		const tabNode = ReactDOM.findDOMNode(tab)
		
		expect(tabNode.querySelectorAll('.tabs-tab').length).toEqual(3)
		expect(tabNode.querySelectorAll('.tabs-tab')[0].classList.contains('tabs-active')).toBe(true)
	})
})