【自动化测试】Jest体验之旅

简介

快速体验

配置文件

Jest CLI 选项

--watchAll

--watch

使用 ES6 模块

简介

Jest 是 Facebook 出品的一个 JavaScript 开源测试框架。相对其他测试框架，其一大特点就是就是内置了常用的测试工具，比如零配置、自带断言、测试覆盖率工具等功能，实现了开箱即用。

Jest 适用但不局限于使用以下技术的项目：Babel,、TypeScript、 Node、 React、Angular、Vue 等。

Jest 主要特点：

零配置
自带断言
作为一个面向前端的测试框架， Jest 可以利用其特有的快照测试功能，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。
此外， Jest 的测试用例是并行执行的，而且只执行发生改变的文件所对应的测试，提升了测试速度。
测试覆盖率
Mock 模拟

快速体验

用你喜欢的软件包管理工具来安装 Jest：

npm install --save-dev jest

给一个假定的函数写测试，这个函数的功能是两数相加。首先创建 sum.js 文件：

function sum(a, b) {
  return a + b;
}
module.exports = sum;

接下来，创建名为 sum.test.js 的文件。这个文件包含了实际测试内容：

const sum = require('./sum');

test('adds 1 + 2 to equal 3', () => {
  expect(sum(1, 2)).toBe(3);
});

将如下代码添加到 package.json 中：

{
  "scripts": {
    "test": "jest"
  }
}

jest 命令会运行项目中所有以 .test.js 结尾的文件

运行测试命令：

npm run test

配置文件

Jest 将根据项目提出一系列问题，并且将创建一个基础配置文件。文件中的每一项都配有简短的说明：

npx jest --init

详细配置信息参考：jestjs.io/docs/zh-Han…

// jest.config.js
/*
 * For a detailed explanation 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 dependency information
  // 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，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 writing coverage reports
  // coverageReporters: [
  //   "json",
  //   "text",
  //   "lcov",
  //   "clover"
  // ],

  // An object that configures minimum threshold enforcement for coverage 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 array of glob patterns
  // forceCoverageMatch: [],

  // A path to a module which exports an async function that is triggered once before all test suites
  // globalSetup: undefined,

  // A path to a module which exports an async function that is triggered once after all test suites
  // globalTeardown: undefined,

  // A set of global variables that need to be available in all test environments
  // globals: {},

  // The maximum amount of workers used to run your tests. Can be specified as % or a number. E.g. maxWorkers: 10% will use 10% of your CPU amount + 1 as the maximum worker number. maxWorkers: 2 will use a maximum of 2 workers.
  // maxWorkers: "50%",

  // An array of directory names to be searched recursively up from the requiring module's 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 arrays of module names that allow to stub out resources with a single module
  // moduleNameMapper: {},

  // An array of regexp pattern strings, matched against all module 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 Jest's configuration
  // preset: undefined,

  // Run tests from one or more projects
  // projects: undefined,

  // Use this configuration option to add custom reporters to Jest
  // reporters: undefined,

  // Automatically reset mock state between every test
  // resetMocks: false,

  // Reset the module registry before running each individual test
  // 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 and modules within
  // rootDir: undefined,

  // A list of paths to directories that Jest should use to search for files in
  // roots: [
  //   "<rootDir>"
  // ],

  // Allows you to use a custom runner instead of Jest's default test runner
  // runner: "jest-runner",

  // The paths to modules that run some code to configure or set up the testing environment before each test
  // setupFiles: [],

  // A list of paths to modules that run some code to configure or set up the testing framework before each test
  // setupFilesAfterEnv: [],

  // The number of seconds after which a test is considered as slow and reported as such in the results.
  // slowTestThreshold: 5,

  // A list of paths to snapshot serializer modules Jest should use 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 against all test paths, matched tests are skipped
  // testPathIgnorePatterns: [
  //   "/node_modules/"
  // ],

  // The regexp pattern or array of patterns that Jest uses to detect 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 is reflected in properties such as location.href
  // testURL: "http://localhost",

  // Setting this value to "fake" allows the use of fake 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 against all source file paths, matched files will skip transformation
  // transformIgnorePatterns: [
  //   "/node_modules/",
  //   "\\.pnp\\.[^\\/]+$"
  // ],

  // An array of regexp pattern strings that are matched against all modules before the module loader will automatically return a mock for them
  // unmockedModulePathPatterns: undefined,

  // Indicates whether each individual test should be reported during the run
  // verbose: undefined,

  // An array of regexp patterns that are matched against all source file paths before re-running tests in watch mode
  // watchPathIgnorePatterns: [],

  // Whether to use watchman for file crawling
  // watchman: true,
};

Jest CLI 选项

参考：jestjs.io/zh-Hans/doc…

--watchAll

监视文件的更改并在任何更改时重新运行所有测试。

jest --watchAll

--watch

该模式需要 Git 支持。

监视 Git 仓库中的文件更改，并重新运行与已更改的文件相关的测试。

jest --watch

使用 ES6 模块

需要使用 Babel，安装所需的依赖。

npm install --save-dev babel-jest @babel/core @babel/preset-env

在工程的根目录下创建一个babel.config.js文件用于配置与你当前Node版本兼容的Babel：

module.exports = {
    presets: [["@babel/preset-env", { targets: { node: "current" } }]],
};

Jest 在运行测试的时候会自动找到 Babel 将 ES6 代码转换为 ES5 执行。

Jest 结合 Babel 的运行原理：运行测试之前，结合 Babel，先把你的代码做一次转化，模块被转换为了 CommonJS，运行转换之后的测试用例代码。

过程：

npm run jest
jest
babel-jest
babel-core
babel 配置文件
转换为 ES5
执行转换之后的测试代码

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