vue 打开一个iframe_Vue 之五 —

单元测试（unit testing）：是指对软件中的最小可测试单元进行检查和验证。代码的终极目标有两个，第一个是实现需求，第二个是提高代码质量和可维护性。单元测试是为了提高代码质量和可维护性，是实现代码的第二个目标的一种方法。对vue组件的测试是希望组件行为符合我们的预期。

本文将从框架选型，环境搭建，使用方式，vue组件测试编写原则四个方面讲述如何在vue项目中落地单元测试。

一、框架选型

cypress / vue-test-utils

选择vue-test-utils 是因为它是官方推荐的vue component 单元测试库。

选择cypress而不是jest 主要是因为：

测试环境的一致性: 在cypress上面跑的测试代码是在浏览器环境上的，而非像jest等在node上的。另外由于cypress在浏览器环境上运行，测试dom相关无需各种mock（如node-canvas等）
统一测试代码风格、避免技术负担: 本身定位 e2e, 但是支持 unit test。
支持CI环境

此外cypress还有很多非常棒的Features，感兴趣的朋友自行参考cypress官方文档。

二、环境搭建

1、安装依赖

npm i cypress @cypress/webpack-preprocessor start-server-and-test nyc babel-plugin-istanbul @vue/test-utils -D

note: 如果是使用vue cli3创建的项目，可以使用

# vue add @vue/cli-plugin-e2e-cypress
# npm i @cypress/webpack-preprocessor start-server-and-test nyc babel-plugin-istanbul @vue/test-utils -D

@cypress/webpack-preprocessor：引入webpack 预处理器

start-server-and-test：启动dev-server 监听端口启动成功，再执行测试命令。cypress 需要dev-server启动才能测试。

nyc babel-plugin-istanbul：覆盖率统计相关

2、添加/修改cypress.json文件

{"baseUrl": "http://localhost:9001","coverageFolder": "coverage","integrationFolder": "src","testFiles": "**/*.spec.js","video": false,"viewportHeight": 900,"viewportWidth": 1600,"chromeWebSecurity": false
}

3、修改package.json配置

"scripts": {"cy:run": "cypress run","cy:open": "cypress open","cy:dev": "start-server-and-test start :9001 cy:open","coverage": "nyc report -t=coverage","test": "rm -rf coverage && start-server-and-test start :9001 cy:run && nyc report -t=coverage"},

4、修改cypress/plugins/index.js（使用vue add @vue/cli-plugin-e2e-cypress的是tests/e2e//plugins/index.js）

// vue cli3 版本
const webpack = require('@cypress/webpack-preprocessor');
const webpackOptions = require('@vue/cli-service/webpack.config');webpackOptions.module.rules.forEach(rule => {if (!Array.isArray(rule.use)) return null;rule.use.forEach(opt => {if (opt.loader === 'babel-loader') {opt.options = {plugins: ['istanbul']};}});
});const options = {webpackOptions,watchOptions: {},
};module.exports = (on, config) => {on('file:preprocessor', webpack(options));return Object.assign({}, config, {integrationFolder: 'src',// screenshotsFolder: 'cypress/screenshots',// videosFolder: 'cypress/videos',// supportFile: 'cypress/support/index.js'})
};
// webpack4 版本const webpack = require('@cypress/webpack-preprocessor');
const config = require('../../webpack.base');
config.mode = 'development';
config.module.rules[0].use.options = {plugins: ['istanbul']
};module.exports = (on) => {const options = {// send in the options from your webpack.config.js, so it works the same// as your app's codewebpackOptions: config,watchOptions: {},};on('file:preprocessor', webpack(options));
};

5、修改cypress/support

// support/index.jsimport './commands';
import './istanbul';

在support目录里添加istanbul.js文件

// https://github.com/cypress-io/cypress/issues/346#issuecomment-365220178
// https://github.com/cypress-io/cypress/issues/346#issuecomment-368832585
/* eslint-disable */
const istanbul = require('istanbul-lib-coverage');const map = istanbul.createCoverageMap({});
const coverageFolder = Cypress.config('coverageFolder');
const coverageFile = `${ coverageFolder }/out-${Date.now()}.json`;Cypress.on('window:before:unload', e => {const coverage = e.currentTarget.__coverage__;if (coverage) {map.merge(coverage);}
});after(() => {cy.window().then(win => {const specWin = win.parent.document.querySelector('iframe[id~="Spec:"]').contentWindow;const unitCoverage = specWin.__coverage__;const coverage = win.__coverage__;if (unitCoverage) {map.merge(unitCoverage);}if (coverage) {map.merge(coverage);}cy.writeFile(coverageFile, JSON.stringify(map));cy.exec('npx nyc report --reporter=html -t=coverage')cy.exec('npm run coverage').then(coverage => {// output coverage reportconst out = coverage.stdout// 替换bash红色标识符.replace(/[31;1m/g, '').replace(/[0m/g, '')// 替换粗体标识符.replace(/[3[23];1m/g, '');console.log(out);}).then(() => {// output html file link to current test reportconst link = Cypress.spec.absolute.replace(Cypress.spec.relative, `${coverageFolder}/${Cypress.spec.relative}`).replace('cypress.spec.', '');console.log(`check coverage detail: file://${link}.html`);});});
});

6、修改package.json (推荐使用git push hooks 里跑test)

"gitHooks": {"pre-push": "npm run test"},"nyc": {"exclude": ["**/*.spec.js","cypress","example"]}

note: 如果项目使用了sass来写css，则必须指定node版本为v8.x.x，这个算是cypress的bug。Issuess

# npm install n -g
# sudo n v8.9.0
# npm rebuild node-sass

这样在git push之前会先跑单元测试，通过了才可以push成功。

三、使用方法

对于各个 utils 内的方法以及 vue组件，只需在其目录下补充同名的 xxx.spec.js，即可为其添加单元测试用例。
断言语法采用 cypress 断言: https://docs.cypress.io/guides/references/assertions.html#Chai
vue组件测试使用官方推荐的test-utils： https://vue-test-utils.vuejs.org/
npm 命令测试：
npm run cy:run （终端测试，前置条件：必须启动本地服务）
npm run cy:open (GUI 测试，前置条件：必须启动本地服务)
npm run cy:dev (GUI测试，自动启动本地服务，成功后打开GUI)
npm run test (终端测试, 自动启动本地服务，并且统计覆盖率，在终端运行，也是CI运行的测试命令)

四、测试原则

1、明白要测试的是什么

不推荐一味追求行级覆盖率，因为它会导致我们过分关注组件的内部实现细节，而只关注其输入和输出。一个简单的测试用例将会断言一些输入 (用户的交互或 prop 的改变) 提供给某组件之后是否导致预期结果 (渲染结果或触发自定义事件)。

2、测试公共接口

a、如果模板有逻辑，我们应该测试它

// template
<button ref="logOutButton" v-if="loggedIn">Log out</button>
// Button.spec.jsconst PropsData = {loggedIn: true,
};it('hides the logOut button if user is not logged in', () => {const wrapper = mount(UserSettingsBar, { PropsData });const { vm } = wrapper;expect(vm.$refs.logOutButton).to.exist();wrapper.setProps({ loggedIn: false });expect(vm.$refs.logOutButton).not.to.exist();
});

原则：Props in Rendered Output

b、什么超出了我们组件的范围

实现细节，过分关注组件的内部实现细节，从而导致琐碎的测试。
测试框架本身, 这是vue应该去做的事情。

1、<p> {{ myProp }} </p>
expect(p.text()).to.be(/ prop value /);2、prop 校验

c、权衡

Integration Test

// Count.spec.jsit('should display the updated count after button is clicked', () => {const wrapper = mount(Count, { count: 0});const ButtonInstance = wrapper.find(Button);const buttonEl = ButtonInstance.find('button')[0]; // find button clickbuttonE1.trigger('click');const CounterDisplayInstance = wrapper.find(CounterDisplay);const displayE1 = CounterDisplayInstance.find('.count-display')[0];expect(displayE1.text()).to.equal('1'); // find display, assert render
});

Shallow Test

// Count.spec.jsit('should pass the "count" prop to CounterDisplay', () => {const counterWrapper = shallow(Counter, {count: 10});const counterDisplayWrapper = counterWrapper.find(CounterDisplay);// we dont't care how this will be renderedexpect(counterDisplayWrapper.propsData().count).to.equal(10);
});it('should update the "count" prop by 1 on Button "increment" event', () => {const counterWrapper = shallow(Counter, {count: 10});const buttonWrapper = counterWrapper.find(Button);// we don't care how this was triggeredbuttonWrapper.vm.$emit('increment');expect(CounterDisplay.propsData().count).to.equal(11);
});

参考：

cypress-vue-unit-test

Vue Test Utils

Component Tests with Vue.js