Jest 基础用法

简单测试

// demo.js

function sum (a, b) {
  return a + b;
}

function subtract (x, y) {
  return x - y;
}

module.exports = {
  sum,
  subtract
}
js

// demo.test.js

// 1. 引入测试函数
const { sum, subtract } = require('./demo');

// 2. 定义函数输入
const result = sum(1, 2);
// 3. 定义预期输出
const expected = 3;

// 4. 检查函数是否返回预期结果
if (result !== expected) {
  throw new Error(`sum(1, 2) result ${ expected }, but get ${ result }`);
}
js

断言和测试用例

定义 expect 断言函数

const { sum, subtract } = require('./demo');

expect(sum(1, 2)).toBe(3);

function expect (result) {
  return {
    toBe (expected) {
      if (result !== expected) {
        throw new Error(`expect result ${ expected }, but get ${ result }`);
      }
    }
  }
}
js

const { sum, subtract } = require('./demo');

expect(sum(1, 2)).toBe(3);
expect(subtract(2, 1)).toBe(1);

function expect (result) {
  return {
    toBe (expected) {
      if (result !== expected) {
        throw new Error(`expect result ${ expected }, but get ${ result }`);
      }
    }
  }
}
js

定义 test 函数，test 函数其实就是测试用例，一个测试用例可以包含多个断言函数。

test('sum(1, 2) result is 3', () => {
  expect(sum(1, 2)).toBe(3);
})
test('subtract(2, 1) result is 1', () => {
  expect(subtract(2, 1)).toBe(1);
})

function test (message, callback) {
  try {
    callback();
  } catch (error) {
    console.error(`${ message }: ${ error }`);
  }
}

function expect (result) {
  return {
    toBe (expected) {
      if (result !== expected) {
        throw new Error(`expect result ${ expected }, but get ${ result }`);
      }
    }
  }
}
js

Jest 体验

安装、使用

初始化 package.json、安装 jest

pnpm init -y

pnpm i jest -D
js

定义 scripts 脚本

// package.json

{
  "scripts": {
    "test": "jest"
  },
}
js

运行测试脚本

pnpm run test
js

 PASS  ./demo.test.js
  √ sum(1, 2) result is 3 (2 ms)
  √ subtract(2, 1) result is 1                                                                                                                                                         
                                                                                                                                                                                       
Test Suites: 1 passed, 1 total                                                                                                                                                         
Tests:       2 passed, 2 total                                                                                                                                                         
Snapshots:   0 total
Time:        0.401 s, estimated 1 s
Ran all test suites.
js

jest 在运行 *.test.js 文件时，会把 test、expect 等相关辅助函数注册到全局环境。

增加代码提示

pnpm i @types/jest -D
js

安装 @types 模块后，可以直接使用 jest 提示，无须引入。

Jest 介绍

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

Jest 使用但不限于以下技术项目：Babel、TypeScript、Node、React、Angular、Vue 等。

Jest 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 等常见框架的自动化测试
Jest 的测试用例是并行执行的，只执行发生改变的文件所对应的测试
测试覆盖率
Mock 模拟

配置文件

Jest 提供默认的零配置的使用方式，不过我们可以通过配置文件的方式去更改默认配置。

生成配置文件

 npx jest --init
js

配置文件中会生成所有配置，不过大部分都是默认配置。

// jest.config.js

/*
 * For a detailed explanation regarding each configuration property, visit:
 * https://jestjs.io/docs/configuration 官方文档地址
 */

module.exports = {
  // All imported modules in your tests should be mocked automatically
  // automock: false,

  // Stop running tests after `n` failures
  // bail: 0,

  // The directory where Jest should store its cached dependency information
  // cacheDirectory: "C:\\Users\\yueluo\\AppData\\Local\\Temp\\jest",

  // Automatically clear mock calls, instances, contexts and results before every test
  clearMocks: true,

  // Indicates whether the coverage information should be collected while executing the test
  // collectCoverage: false,

  // An array of glob patterns indicating a set of files for which coverage information should be collected
  // collectCoverageFrom: undefined,

  // The directory where Jest should output its coverage files
  // coverageDirectory: undefined,

  // An array of regexp pattern strings used to skip coverage collection
  // coveragePathIgnorePatterns: [
  //   "\\\\node_modules\\\\"
  // ],

  // Indicates which provider should be used to instrument code for coverage
  // 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,

  // The default configuration for fake timers
  // fakeTimers: {
  //   "enableGlobally": 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",
  //   "mjs",
  //   "cjs",
  //   "jsx",
  //   "ts",
  //   "tsx",
  //   "json",
  //   "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 before 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 and implementation before 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: "jsdom",

  // Options that will be passed to the testEnvironment
  // testEnvironmentOptions: {},

  // Adds a location field to test results
  // testLocationInResults: false,

  // 默认文件配置规则
  // The glob patterns Jest uses to detect test files
  // testMatch: [
  //   "**/__tests__/**/*.[jt]s?(x)",
  //   "**/?(*.)+(spec|test).[tj]s?(x)"
  // ],

  // 默认忽略目录
  // 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: "jest-circus/runner",

  // 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,
};
js

// jest.config.js

/*
 * For a detailed explanation regarding each configuration property, visit:
 * https://jestjs.io/docs/configuration 官方文档地址
 */

module.exports = {
  // All imported modules in your tests should be mocked automatically
  // automock: false,

// Stop running tests after `n` failures
  // bail: 0,

// The directory where Jest should store its cached dependency information
  // cacheDirectory: "C:\\Users\\yueluo\\AppData\\Local\\Temp\\jest",

// Automatically clear mock calls, instances, contexts and results before every test
  clearMocks: true,

// Indicates whether the coverage information should be collected while executing the test
  // collectCoverage: false,

// An array of glob patterns indicating a set of files for which coverage information should be collected
  // collectCoverageFrom: undefined,

// The directory where Jest should output its coverage files
  // coverageDirectory: undefined,

// An array of regexp pattern strings used to skip coverage collection
  // coveragePathIgnorePatterns: [
  //   "\\\\node_modules\\\\"
  // ],

// Indicates which provider should be used to instrument code for coverage
  // 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,

// The default configuration for fake timers
  // fakeTimers: {
  //   "enableGlobally": 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",
  //   "mjs",
  //   "cjs",
  //   "jsx",
  //   "ts",
  //   "tsx",
  //   "json",
  //   "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 before 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 and implementation before 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: "jsdom",

// Options that will be passed to the testEnvironment
  // testEnvironmentOptions: {},

// Adds a location field to test results
  // testLocationInResults: false,

// 默认文件配置规则
  // The glob patterns Jest uses to detect test files
  // testMatch: [
  //   "**/__tests__/**/*.[jt]s?(x)",
  //   "**/?(*.)+(spec|test).[tj]s?(x)"
  // ],

// 默认忽略目录
  // 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: "jest-circus/runner",

// 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,
};

JestCli 选项

Jest 不仅可以通过配置文件配置，还可以通过命令行参数进行配置。

// a.test.js

test('test a', () => {
  console.log('this a');
})
js

// demo.test.js

const { sum, subtract } = require('./demo');

test('sum(1, 2) result is 3', () => {
  expect(sum(1, 2)).toBe(3);
})
test('subtract(2, 1) result is 1', () => {
  expect(subtract(2, 1)).toBe(1);
})
js

直接运行 pnpm run test 会执行所有的测试用例。

> 02@1.0.0 test
> jest

 PASS  ./a.test.js
  ● Console

    console.log
      this a

      at Object.log (a.test.js:2:11)

 PASS  ./demo.test.js

Test Suites: 2 passed, 2 total
Tests:       3 passed, 3 total
Snapshots:   0 total
Time:        1.58 s
Ran all test suites.
js

我们还可以指定需要测试的文件

// package.json

{
  "scripts": {
    "test": "jest",
    "test2": "jest demo.test.js"
  }
}
js

执行 pnpm run test2 只会执行 demo.test.js 文件。

 PASS  ./demo.test.js
  √ sum(1, 2) result is 3 (1 ms)
  √ subtract(2, 1) result is 1                                                   
                                                                                 
Test Suites: 1 passed, 1 total                                                   
Tests:       2 passed, 2 total                                                   
Snapshots:   0 total
Time:        0.454 s, estimated 1 s
Ran all test suites matching /demo.test.js/i.
js

现在 jest 只会在手动执行的时候触发，如果我们向实时监听文件变化可以这样配置。

// package.json

{
  "scripts": {
		// ...
    "test:watch": "jest --watchAll"
  }
}
js

运行脚本文件，jest 就会监听所有文件的执行。

> 02@1.0.0 test
> jest

 PASS  ./a.test.js
  ● Console

    console.log
      this a

      at Object.log (a.test.js:2:11)

 PASS  ./demo.test.js
 PASS  ./a.test.js
  ● Console

    console.log
      this a

      at Object.log (a.test.js:2:11)


Test Suites: 2 passed, 2 total
Tests:       3 passed, 3 total
Snapshots:   0 total
Time:        1.109 s
Ran all test suites.

Watch Usage
 › Press f to run only failed tests.
 › Press o to only run tests related to changed files.
 › Press p to filter by a filename regex pattern.
 › Press t to filter by a test name regex pattern.
 › Press q to quit watch mode.
 › Press Enter to trigger a test run.
js

建议开发过程中使用 watch 模式，可以实时给予反馈。

监视模式

–watchAll

监视文件的更改并在任何更改时重新运行所有的测试文件。

jest --watchAll
js

–watch

该模式需要 Git 支持

监视 Git 仓库中的文件更改，并重新运行已更改文件相关的测试。如果文件未更改，不会执行任何测试文件。

jest --watch
js

监视模式的服务命令

执行 jest --watchAll 后，会打印出如下内容：

Watch Usage
 › Press f to run only failed tests.
 › Press o to only run tests related to changed files.
 › Press p to filter by a filename regex pattern.
 › Press t to filter by a test name regex pattern.
 › Press q to quit watch mode.
 › Press Enter to trigger a test run.
js

执行脚本后，可以通过键盘控制 jest。

f：只运行失败的测试
o：只运行与更改文件相关的测试，即 watch模式（需要 git 支持）
a：运行所有的测试，即 watchAll 模式
p：以文件名正则表达式模式进行过滤
- 只有 --watchAll 的时候 p 模式才生效
- 注意：testRegex 将尝试使用绝对路径的方式来检测
t：根据测试名称进行过滤，即 test('sum') ，sum 就是测试名称
q：退出监视模式
enter：触发测试重新执行

使用 ES6 模块

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。

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 CommonJS，运行转换后的测试用例代码。

pnpm install babel-jest @babel/core @babel/preset-env -D
js

// babel.config.js

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

// demo.js
export function sum (a, b) {
  return a + b;
}

export function subtract (x, y) {
  return x - y;
}
js

// demo.test.js
import { sum, subtract } from './demo';

test('sum(1, 2) result is 3', () => {
  expect(sum(1, 2)).toBe(3);
})
test('subtract(2, 1) result is 1', () => {
  expect(subtract(2, 1)).toBe(1);
})
js

执行脚本文件 pnpm run test2 可以正常运行。

> 02@1.0.0 test2 D:\workspace\notes\jest\02
> jest demo.test.js

 PASS  ./demo.test.js
  √ sum(1, 2) result is 3 (1 ms)
  √ subtract(2, 1) result is 1                                                                                                                                                         
                                                                                                                                                                                       
Test Suites: 1 passed, 1 total                                                                                                                                                         
Tests:       2 passed, 2 total                                                                                                                                                         
Snapshots:   0 total
Time:        2.086 s
Ran all test suites matching /demo.test.js/i.
js

总结

本篇文章我们学习了 Jest 的基础使用，这部分内容希望你可以熟练掌握。