前端自动化测试：Jest 测试框架应用
Jest : https://jestjs.io/zh-Hans/是前端 Facebook 出品的一个 JavaScript 开源测试框架。
相对其他测试框架，自动其一大特点就是化测就是内置了常用的测试工具，比如零配置、试J试框自带断言、前端测试覆盖率工具等功能，自动实现了开箱即用。化测
Jest 适用但不局限于使用以下技术的试J试框项目：Babel、TypeScript、前端 Node、自动 React、化测Angular、试J试框Vue 等。前端
Jest 主要特点：
零配置 自带断言 作为一个面向前端的自动测试框架， Jest 可以利用其特有的化测快照测试功能，通过比对UI 代码生成的快照文件，实现对 React 等常见前端框架的自动测试。 Jest 的测试用例是并行执行的，而且只执行发生改变的服务器租用文件所对应的测试，提升了测试速度。 测试覆盖率 Mock 模拟快速体验 Jest
安装 Jest 到项目中：
npm install --save-dev jest //math.js functionadd (a, b) { return a * b } functionsubtract (x, y) { return x - y } module.exports= { add, subtract } //test.js ==> math.test.js const { add, subtract } =require(./math) test(测试加法, () => { expect(add(1,2)).toBe(3) }) test(测试减法, () => { expect(subtract(2,1)).toBe(1) }) //package.json { "scripts":{ "test":"jest" } }jest 命令会运行项目中所有以 .test.js 结尾的文件
最后运行测试命令：
npm run test解析：
jest 找到项目中所有以 .test.js 结尾的文件并运行 jest 会给测试文件提供 test、expect 等全局函数，所以在测试文件中可以直接使用 jest 为测试结果提供了良好的日志输出解决 vscode 中 jest 代码提示问题
npm i -D @types/jest注意：@types/jest 必须安装到项目的根目录，并且以根目录的方式在 vscode 中打开，否则不生效。或者说只要是 vscode 打开的项目根目录有 @types/jest 这个包就可以了。
配置文件
npx jest--init配置文件生成选项：
是否使用 ts ; 使用哪种测试环境; 使用 jest 收集测试覆盖率报告; 使用那种引擎检测覆盖率：v8 处于实验性阶段，建议 Node v14 后使用，babel 较为成熟 每次测试时，是否自动清除 mock 实例;详细配置信息参考：https://jestjs.io/docs/zh-Hans/configuration。
//jest.config.js /* * For a detailedexplanation regarding each configuration property, visit: *https://jestjs.io/docs/en/configuration.html */ module.exports= { // 自动 mock 所有导入的外部模块 // automock: false, // 在指定次数失败后停止运行测试 // bail: 0, // The directory where Jest should store its cached dependencyinformation // cacheDirectory:"/private/var/folders/5h/_98rffpj1z95b_0dm76lvzm40000gn/T/jest_dx", // 在每个测试之间自动清除 mock 调用和实例 clearMocks:true, // 是否收集测试覆盖率信息 // collectCoverage: false, // 一个 glob 模式数组，指示应该为其收集覆盖率信息的一组文件 // collectCoverageFrom: undefined, // 测试覆盖率报错文件输出的目录 coverageDirectory:"coverage", // 忽略测试覆盖率统计 // coveragePathIgnorePatterns: [ // "/node_modules/" // ], // 指示应该使用哪个提供程序检测代码的覆盖率，默认是 babel，源码库可选 v8，但是 v8 不太稳定，建议Node 14 以上版本使用 // coverageProvider: "babel", // A list of reporter names that Jest uses when writingcoverage reports // coverageReporters: [ // "json", // "text", // "lcov", // "clover" // ], // An object that configures minimum threshold enforcement forcoverage results // coverageThreshold: undefined, // A path to a custom dependency extractor // dependencyExtractor: undefined, // Make calling deprecated APIs throw helpful error messages // errorOnDeprecated: false, // Force coverage collection from ignored files using an arrayof glob patterns // forceCoverageMatch: [], // A path to a module which exports an async function that istriggered once before all test suites // globalSetup: undefined, // A path to a module which exports an async function that istriggered once after all test suites // globalTeardown: undefined, // A set of global variables that need to be available in alltest environments // globals: { }, // The maximum amount of workers used to run your tests. Canbe specified as % or a number. E.g. maxWorkers: 10% will use 10% of your CPUamount + 1 as the maximum worker number. maxWorkers: 2 will use a maximum of 2workers. // maxWorkers: "50%", // An array of directory names to be searched recursively upfrom the requiring modules location // moduleDirectories: [ // "node_modules" // ], // An array of file extensions your modules use // moduleFileExtensions: [ // "js", // "json", // "jsx", // "ts", // "tsx", // "node" // ], // A map from regular expressions to module names or to arraysof module names that allow to stub out resources with a single module // moduleNameMapper: { }, // An array of regexp pattern strings, matched against allmodule paths before considered visible to the module loader // modulePathIgnorePatterns: [], // Activates notifications for test results // notify: false, // An enum that specifies notification mode. Requires { notify: true } // notifyMode: "failure-change", // A preset that is used as a base for Jests configuration // preset: undefined, // Run tests from one or more projects // projects: undefined, // Use this configuration option to add custom reporters toJest // reporters: undefined, // Automatically reset mock state between every test // resetMocks: false, // Reset the module registry before running each individualtest // resetModules: false, // A path to a custom resolver // resolver: undefined, // Automatically restore mock state between every test // restoreMocks: false, // The root directory that Jest should scan for tests andmodules within // rootDir: undefined, // A list of paths to directories that Jest should use tosearch for files in // roots: [ // "<rootDir>" // ], // Allows you to use a custom runner instead of Jests defaulttest runner // runner: "jest-runner", // The paths to modules that run some code to configure or setup the testing environment before each test // setupFiles: [], // A list of paths to modules that run some code to configureor set up the testing framework before each test // setupFilesAfterEnv: [], // The number of seconds after which a test is considered asslow and reported as such in the results. // slowTestThreshold: 5, // A list of paths to snapshot serializer modules Jest shoulduse for snapshot testing // snapshotSerializers: [], // The test environment that will be used for testing // testEnvironment: "jest-environment-jsdom", // Options that will be passed to the testEnvironment // testEnvironmentOptions: { }, // Adds a location field to test results // testLocationInResults: false, // The glob patterns Jest uses to detect test files // testMatch: [ // "**/__tests__/**/*.[jt]s?(x)", // "**/?(*.)+(spec|test).[tj]s?(x)" // ], // An array of regexp pattern strings that are matched againstall test paths, matched tests are skipped // testPathIgnorePatterns: [ // "/node_modules/" // ], // The regexp pattern or array of patterns that Jest uses todetect test files // testRegex: [], // This option allows the use of a custom results processor // testResultsProcessor: undefined, // This option allows use of a custom test runner // testRunner: "jasmine2", // This option sets the URL for the jsdom environment. It isreflected in properties such as location.href // testURL: "http://localhost", // Setting this value to "fake" allows the use offake timers for functions such as "setTimeout" // timers: "real", // A map from regular expressions to paths to transformers // transform: undefined, // An array of regexp pattern strings that are matched againstall source file paths, matched files will skip transformation // transformIgnorePatterns: [ // "/node_modules/", // "\\.pnp\\.[^\\/]+$" // ], // An array of regexp pattern strings that are matched againstall modules before the module loader will automatically return a mock for them // unmockedModulePathPatterns: undefined, // Indicates whether each individual test should be reportedduring the run // verbose: undefined, // An array of regexp patterns that are matched against allsource file paths before re-running tests in watch mode // watchPathIgnorePatterns: [], // Whether to use watchman for file crawling // watchman: true, };Jest CLI Options
参考：https://jestjs.io/zh-Hans/docs/cli
指定测试文件运行
"scripts":{ "test":"jest ./math.test.js" },Jest 监视模式
--watchAll 选项：监视文件的更改并在任何更改时重新运行所有测试。
"scripts": { "test": "jest --watchAll" },Jest API
在测试文件中，Jest 将所有这些方法和对象放入全局环境中。无需要求或导入任何内容即可使用它们。但是，如果喜欢显式导入，则可以：
import { describe, expect, test } from@jest/globalsTest 函数
test 函数别名：it(name, fn, timeout)。
test(name,fn, timeout) test.concurrent(name, fn, timeout) test.concurrent.each(table)(name, fn, timeout) test.concurrent.only.each(table)(name, fn) test.concurrent.skip.each(table)(name, fn) test.each(table)(name, fn, timeout) test.only(name, fn, timeout)只运行当前测试用例
test.only.each(table)(name, fn) test.skip(name,fn) test.skip.each(table)(name, fn) test.todo(name)创建 global-api.test.js 测试文件，注意，测试文件中必须有一个测试用例，如果没有则直接报错。
test(should , () => { console.log(test--api) }) test(should , () => { console.log(test--api) }) test(should1 , () => { console.log(test--api1) }) // 上面两个不运行 test.only(should2 , () => { console.log(test--api2) })Expect 匹配器
在编写测试时，通常需要检查值是否满足某些条件。Expect 让我们可以访问许多“匹配器”，以验证不同的内容。
test(two plus two is four, () => { expect(2+2).toBe(6) expect({ name:jack }).toEqual({ name:jack }) expect(Christoph).toMatch(/stop/) expect(4).toBeGreaterThan(3) expect(4).toBeLessThan(5) })完整的匹配器列表查看：https://jestjs.io/zh-Hans/docs/expect
describe 函数
describe 创建一个将几个相关测试组合在一起的块。
const myBeverage = { delicious:true, sour:false, }; describe(my beverage, () => { test(is delicious, () => { expect(myBeverage.delicious).toBeTruthy(); }); test(is not sour, () => { expect(myBeverage.sour).toBeFalsy(); }); });分组最直观的就是在测试提示中，有更加友好的信息输出。
describe(name,fn) describe.each(table)(name, fn, timeout) describe.only(name,fn) describe.only.each(table)(name, fn) describe.skip(name,fn) describe.skip.each(table)(name, fn)云服务器