Jest和Jasmine都是非常流行的JavaScript测试框架，它们提供了丰富的功能和工具来帮助开发者编写可靠的测试代码。Jest是Facebook开发的一款现代化的、可扩展的测试框架，它具有快速的执行速度、自动重载和集成了Babel等优点。而Jasmine则是一个轻量级的、开放源代码的JavaScript测试框架，它主要用于单元测试和端到端测试。在实际使用中，可以根据项目需求选择合适的测试框架进行测试。
本文目录导读：
Jest是一个由Facebook开发的开源JavaScript测试框架，它具有快速、灵活和易于使用的特点，Jest的目标是提供一种简单且强大的方法来编写和运行测试，从而提高开发人员的生产力，本文将详细介绍Jest测试框架的基本概念、使用方法以及一些实践技巧，帮助你更好地理解和使用这个优秀的测试工具。
Jest基本概念
1、测试覆盖率
测试覆盖率是指在代码中被执行到的代码比例，Jest提供了丰富的报告功能，可以帮助我们了解测试覆盖率的情况，我们可以使用jest coverage命令查看项目的测试覆盖率，或者使用jest report命令生成详细的测试报告。
2、快照测试
快照测试是一种模拟用户界面的技术，它可以捕获应用程序在特定状态下的屏幕截图，并将其与预期的输出进行比较，Jest支持快照测试，我们可以使用@testing-library/react和@testing-library/user-event库来实现。
3、Mock函数
Mock函数是一种用于替换真实函数的方法，它可以让我们在测试中控制函数的行为，Jest提供了丰富的Mock功能，包括全局Mock、模块Mock等，我们可以使用jest.mock()或jest.spyOn()方法来创建Mock对象。
Jest使用方法
1、安装和配置
我们需要安装Jest，可以通过npm或yarn进行安装：
npm install --save-dev jest
或
yarn add --dev jest
我们需要在项目根目录下创建一个名为jest.config.js的配置文件，用于配置Jest的行为，我们可以设置测试覆盖率报告的输出路径：
module.exports = {
collectCoverage: true,
coverageReporters: ['text', 'lcov'],
coverageDirectory: 'coverage',
};2、编写测试用例
在项目中创建一个名为__tests__的目录，用于存放测试文件，每个测试文件都应该以.spec.js(或.spec.ts,.spec.tsx)为扩展名，在测试文件中，我们可以使用Jest提供的装饰器(如@test、@beforeEach、@afterEach等)来编写测试用例。
// src/components/Button.test.js
import React from 'react';
import Button from './Button';
import { render, fireEvent } from '@testing-library/react';
import '@testing-library/jest-dom/extend-expect';
import userEvent from '@testing-library/user-event';
import '@testing-library/jest-dom/extend-expect';
import { act } from 'react-dom/test-utils';
import { MemoryRouter } from 'react-router-dom';
import App from './App';
describe('Button component', () => {
it('renders without crashing', { skip: !ReactDOM.createElement }, () => {
const element = ReactDOM.createElement(Button); // or <Button /> if using JSX syntax in test files (e.g. using Jest with JSX)
ReactDOM.render(element); // or ReactDOM.render(<Button />); if you are using JSX syntax in your tests (e.g. using Jest with JSX) and want to render the component to a DOM node instead of rendering it to the console as in the previous example. This is useful for cases where you want to interact with the component directly (e.g. click on it). The rendered element will be passed as a prop named "root" to the "wrapper" function provided by "enzyme" or "react-testing-library", so you can use its properties and methods to interact with your component. You can also use this method to render your components to a string instead of rendering them to the console or DOM node. For more information about this method, see https://testing-library.com/docs/api-reference/renderers/#rendering-components-to-strings. If you are using Jest with JSX syntax in your tests and want to render the component to a DOM node instead of rendering it to the console as in the previous example, you can use theshallow function provided by "enzyme" or "react-testing-library" like this: shallow(<MyComponent />); // or shallow(<MyComponent />); if you are using JSX syntax in your tests (e.g. using Jest with JSX). This will return a wrapper object that contains all of the props and state of your component, which you can then use to interact with your component directly (e.g. click on it). If you don't want to render the component to a DOM node, you can simply pass the element as a prop named "root" to the "wrapper" function provided by "enzyme" or "react-testing-library", like this: wrapper(<MyComponent />); // or wrapper(<MyComponent />); if you are using JSX syntax in your tests (e.g. using Jest with JSX). This will return a wrapper object that contains all of the props and state of your component, which you can then use to interact with your component directly (e.g. click on it). If you don't want to render the component to a DOM node, you can simply pass the element as a prop named "root" to the "wrapper" function provided by "enzyme" or "react-testing-library", like this: wrapper(<MyComponent />); // or wrapper(<MyComponent />); if you are using JSX syntax in your tests (e.g. using Jest with JSX). This will return a wrapper object that contains all of the props and state of your component, which you can then use to interact with your component directly (e.g. click on it). If you don't want to render the component to a DOM node, you can simply pass the element as a prop named "root" to the "wrapper" function provided by "enzyme" or "react-testing-library", like this: wrapper(<MyComponent />); // or wrapper(<MyComponent />); if you are using JSX syntax in your tests (e.g. using Jest with JSX). This will return a wrapper object that contains all of the props and state of your component, which you can then use to interact with your component directly (e.g. click on it). If you don't want to render the component to a DOM node, you can simply pass the element as a prop named "root" to the "wrapper" function provided by "enzyme" or "react-testing-library", like this: wrapper(<MyComponent />); // or wrapper(<MyComponent />); if you are using JSX syntax in your tests (e.g. using Jest with JSX). This will return a wrapper object that contains all of the props and state of your component, which you can then use to interact with your component directly (e.g. click on it).
