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class="tocCollapsible_ETCw theme-doc-toc-mobile tocMobile_ITEo"><button type="button" class="clean-btn tocCollapsibleButton_TO0P">On this page</button></div><div class="theme-doc-markdown markdown"><h1>如何对前端代码实施测试</h1><h2 class="anchor anchorWithHideOnScrollNavbar_WYt5" id="相关问题">相关问题<a href="#相关问题" class="hash-link" aria-label="Direct link to 相关问题" title="Direct link to 相关问题"></a></h2><ul><li>你是如何看待软件测试的？</li><li>你在工作中是如何实施测试的？</li><li>对前端代码进行测试，有哪些测试方法？</li><li>说说你对测试驱动开发的理解？</li></ul><h2 class="anchor anchorWithHideOnScrollNavbar_WYt5" id="回答关键点">回答关键点<a href="#回答关键点" class="hash-link" aria-label="Direct link to 回答关键点" title="Direct link to 回答关键点"></a></h2><p><code>Unit Tests</code> <code>E2E Tests</code> <code>测试覆盖率</code> <code>TDD</code> <code>BDD</code></p><p>测试是保障代码质量的重要手段，可以验证我们代码的正确性；测试可以增强我们在修改代码时的信心，保证代码重构的正确性；编写测试还有助于理解业务功能，避免在编写代码时做出过度的设计；对于开发人员来说，测试用例还是最好的开发文档。测试的分类方法有很多种，一般按测试阶段可以分为单元测试（Unit Tests）、集成测试（Integration Tests）、E2E 测试（端到端测试，End-to-End Tests）来保障产品关键路径的可靠性。</p><p>一般来说，测试代码由大量的单元测试，适中的集成测试，以及少量的 E2E 测试构成。</p><p>测试驱动开发（TDD）是一种通过编写测试来指导软件的开发过程，构建软件的技术。</p><h2 class="anchor anchorWithHideOnScrollNavbar_WYt5" id="知识点深入">知识点深入<a href="#知识点深入" class="hash-link" aria-label="Direct link to 知识点深入" title="Direct link to 知识点深入"></a></h2><h3 class="anchor anchorWithHideOnScrollNavbar_WYt5" id="测试的种类">测试的种类<a href="#测试的种类" class="hash-link" aria-label="Direct link to 测试的种类" title="Direct link to 测试的种类"></a></h3><p>从不同的角度对待测试，会有不同的分类方法，例如白盒测试、回归测试、灰度测试、冒烟测试等。以下主要关注测试阶段。按测试的不同目标，在代码中进行以下三种自动化测试：</p><p>这三种测试构成测试金字塔，从 E2E 测试到单元测试，集成度越来越低、隔离度越来越高，运行测试所需要的时间也越来越短。
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<img loading="lazy" src="https://user-images.githubusercontent.com/4338052/165334296-ecb4e75d-d166-4735-bf82-c2a96279dbe5.png" alt="image" class="img_ev3q"></p><p><strong>单元测试</strong></p><p>是指对软件中独立单元（通常是一个函数、一个模块或一组紧密关联的功能集合）进行测试的方法。单元测试至少应该对模块暴露的公共接口进行测试，同时不应与代码的具体实现耦合得太紧密（如 Element 的 classname）。单元测试中经常会用到被称为 Mocks 或 Stubs 的 fake 实现，这可以使测试免于影响真实的系统，或者让测试运行得更快。</p><p>关于测试的 mock，一般有两种不同的意见：一派认为对当前测试点关注之外的东西都可以进行 mock，以实现完美的隔离，来达到避免副作用和进行复杂的测试环境设置的目的；另一派认为要尽量少的在测试中使用 mock，因为 mock 可能与真实的接口存在不一致的地方，而这很难察觉到。在实际的工作中，都会综合考虑这两派的意见，合理谨慎的运用 mock。通常测试覆盖率达到 100% 并不意味着软件就是绝对可靠的。</p><p><strong>集成测试</strong></p><p>一个完整的软件通常需要很多子系统配合工作。比如对后端来说，包含数据库、文件系统及其他网络调用；对前端来说，包含 UI 组件，数据仓库，网络请求等。正如单元测试难以精确界定一个单元的范围一样，集成测试在边界的确定中比单元测试更加模糊。集成测试一般是指对系统和外部功能的集成整体进行的测试。</p><p>另一方面，集成测试的含义通常比单元测试更模糊，如何确定测试的边界往往随着项目的具体情况而各有不同。集成测试中通常有着和单元测试重复的部分。有一种观点是认为可以用契约测试（Contract Tests）代替部分集成测试。</p><p>在现代化的组织架构中，随着软件的规模越来越大，开发部门也会分成各个规模较小的团队，各自负责相对独立的部分，构建高内聚、低耦合的服务。不同的服务之间通常是通过接口互相通信的，比如通过 HTTP 进行 REST 通信，使用 gRPC 来进行 RPC 通信，或者使用消息队列来进行通信。这时，可以考虑使用契约测试，来对各个子系统提供的接口进行测试。</p><div></div><p><strong>E2E 测试</strong></p><p>测试金字塔的最顶端一般是 E2E 测试，在进行测试时，一般有测试人员手动进行的测试，也有自动化的工具进行的测试。</p><p>E2E 测试中的一条用例会覆盖一条完整的用户操作流程。对于 web 程序来说，我们会测试用户的输入是否触发了正确的动作、数据是否呈现给了用户、UI 状态是否按照预期改变等等。</p><p>Web 应用程序的 E2E 测试通常是使用 WebDriver 来驱动实际的浏览器运行来进行测试的，这通常意味着 E2E 测试会很慢。所以我们在功能点能够被前面两种测试覆盖的时候，尽量采用它们来进行测试。</p><h3 class="anchor anchorWithHideOnScrollNavbar_WYt5" id="如何编写测试">如何编写测试<a href="#如何编写测试" class="hash-link" aria-label="Direct link to 如何编写测试" title="Direct link to 如何编写测试"></a></h3><p>最理想的状态是践行测试驱动开发，采用先红后绿的流程开发软件。这比写完功能代码后再补充测试要好，因为后补测试用例是在功能代码已经完成的情况下进行的，这也就是所谓的白盒测试。</p><p>白盒测试可能面临某些思维盲点（例如一旦从一堆不规则的图形中找出了五角星，后面再次看到时就很难再忽略它了），可能会导致测试覆盖的不够全面。白盒测试也可能过多的测试边缘情况，而忽略了业务主流程。
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||
<img loading="lazy" src="https://user-images.githubusercontent.com/4338052/164974483-2a382312-1b02-4336-87fa-02c7d6679542.png" alt="image" class="img_ev3q"></p><blockquote><p>图片来源 <a href="https://insights.thoughtworks.cn/test-like-user-1/" target="_blank" rel="noopener noreferrer">像用户一样测试：打破知识诅咒</a></p></blockquote><p>TDD 有四个关键点：</p><ol><li>思考（Think）：对业务需求进行拆解，将需求分解为有上下文、行为和预期结果的一个或多个任务列表，并保证列表中的每个任务是简单的、能快速实现的。</li><li>红（Red bar）：从上一步的任务列表中挑选任务，为该任务快速的编写测试代码，然后不断循环的完成所有任务到测试用例的转换。此时，运行测试代码时的断言是会失败的。</li><li>绿（Green bar）：以最快的速度让测试变绿，这通常意味着不需要考虑复杂的设计模式，不做过度设计，不写多余的代码，只需要符合一些简单的设计原则就行了。</li><li>重构（Refactor）：在上面所有的测试都通过以后，现在可以对代码开始重构（识别代码中的坏味道（Code smell）、应用更健壮的设计模式等），而不必担心破坏之前的功能。</li><li>当准备好添加新的功能时，重新开始上面的循环。不断添加小的增量是实践 TDD 的关键。</li></ol><div></div><h4 class="anchor anchorWithHideOnScrollNavbar_WYt5" id="测试的结构">测试的结构<a href="#测试的结构" class="hash-link" aria-label="Direct link to 测试的结构" title="Direct link to 测试的结构"></a></h4><p>对于所有的测试代码，一般都会遵循以下的结构。</p><ol><li>设置测试数据。</li><li>调用测试方法。</li><li>断言期望的结果已经返回。</li></ol><p>这个结构通常被记为 "Arrange, Act, Assert" 的 3A 短语。另外有一个来自 BDD（行为驱动开发）的一组短语是 "Given, When, Then"。</p><h4 class="anchor anchorWithHideOnScrollNavbar_WYt5" id="测试工具">测试工具<a href="#测试工具" class="hash-link" aria-label="Direct link to 测试工具" title="Direct link to 测试工具"></a></h4><p><strong>单元测试工具</strong></p><p>测试框架：常用的测试框架有 Jest，Mocha，Jasmine，AVA 等，大部分测试框架都提供了类似的功能，一般包括以下这些方面：</p><ul><li>测试块的组织，比如 describe 和 it/test 语法。</li><li>每个 describe 块的 before<!-- -->[All]<!-- -->，after<!-- -->[All]<!-- -->，beforeEach，afterEach 钩子。</li><li>全局的 setup 和 teardown 设置。</li><li>匹配语法，各个框架一般拥有相似的接口，而这个风格一般继承自 Chai 这个框架。</li><li>Mock 功能的支持，对定时器的 mock、对函数的 mock、对模块的 mock。</li></ul><p>被 Chai 发扬光大的三种匹配语法：</p><div class="language-js codeBlockContainer_Ckt0 theme-code-block" style="--prism-color:#393A34;--prism-background-color:#f6f8fa"><div class="codeBlockContent_biex"><pre tabindex="0" class="prism-code language-js codeBlock_bY9V thin-scrollbar"><code class="codeBlockLines_e6Vv"><span class="token-line" style="color:#393A34"><span class="token comment" style="color:#999988;font-style:italic">// Assert 经典语法，提供了对被测试对象的各个维度的断言语法。</span><span class="token plain"></span><br></span><span class="token-line" style="color:#393A34"><span class="token plain">assert</span><span class="token punctuation" style="color:#393A34">.</span><span class="token method function property-access" style="color:#d73a49">typeOf</span><span class="token punctuation" style="color:#393A34">(</span><span class="token plain">foo</span><span class="token punctuation" style="color:#393A34">,</span><span class="token plain"> </span><span class="token string" style="color:#e3116c">"string"</span><span class="token punctuation" style="color:#393A34">)</span><span class="token punctuation" style="color:#393A34">;</span><span class="token plain"></span><br></span><span class="token-line" style="color:#393A34"><span class="token plain">assert</span><span class="token punctuation" style="color:#393A34">.</span><span class="token method function property-access" style="color:#d73a49">equal</span><span class="token punctuation" style="color:#393A34">(</span><span class="token plain">foo</span><span class="token punctuation" style="color:#393A34">,</span><span class="token plain"> </span><span class="token string" style="color:#e3116c">"bar"</span><span class="token punctuation" style="color:#393A34">)</span><span class="token punctuation" style="color:#393A34">;</span><span class="token plain"></span><br></span><span class="token-line" style="color:#393A34"><span class="token plain">assert</span><span class="token punctuation" style="color:#393A34">.</span><span class="token method function property-access" style="color:#d73a49">lengthOf</span><span class="token punctuation" style="color:#393A34">(</span><span class="token plain">foo</span><span class="token punctuation" style="color:#393A34">,</span><span class="token plain"> </span><span class="token number" style="color:#36acaa">3</span><span class="token punctuation" style="color:#393A34">)</span><span class="token punctuation" style="color:#393A34">;</span><span class="token plain"></span><br></span><span class="token-line" style="color:#393A34"><span class="token plain">assert</span><span class="token punctuation" style="color:#393A34">.</span><span class="token method function property-access" style="color:#d73a49">property</span><span class="token punctuation" style="color:#393A34">(</span><span class="token plain">tea</span><span class="token punctuation" style="color:#393A34">,</span><span class="token plain"> </span><span class="token string" style="color:#e3116c">"flavors"</span><span class="token punctuation" style="color:#393A34">)</span><span class="token punctuation" style="color:#393A34">;</span><span class="token plain"></span><br></span><span class="token-line" style="color:#393A34"><span class="token plain">assert</span><span class="token punctuation" style="color:#393A34">.</span><span class="token method function property-access" style="color:#d73a49">lengthOf</span><span class="token punctuation" style="color:#393A34">(</span><span class="token plain">tea</span><span class="token punctuation" style="color:#393A34">.</span><span class="token property-access">flavors</span><span class="token punctuation" style="color:#393A34">,</span><span class="token plain"> </span><span class="token number" style="color:#36acaa">3</span><span class="token punctuation" style="color:#393A34">)</span><span class="token punctuation" style="color:#393A34">;</span><span class="token plain"></span><br></span><span class="token-line" style="color:#393A34"><span class="token plain" style="display:inline-block"></span><br></span><span class="token-line" style="color:#393A34"><span class="token plain"></span><span class="token comment" style="color:#999988;font-style:italic">// 下面两种都是 BDD 风格的断言方式，它们都使用了更接近自然表达的语法来进行匹配。</span><span class="token plain"></span><br></span><span class="token-line" style="color:#393A34"><span class="token plain"></span><span class="token comment" style="color:#999988;font-style:italic">// 在 node.js 和现代浏览器中，它们几乎没有区别。</span><span class="token plain"></span><br></span><span class="token-line" style="color:#393A34"><span class="token plain"></span><span class="token comment" style="color:#999988;font-style:italic">// Should 采用了修改 Object 原型的方式实现到链式语法，这可能在古老的 IE 浏览器或某些嵌入式 JS 运行时中不能正常工作。</span><span class="token plain"></span><br></span><span class="token-line" style="color:#393A34"><span class="token plain" style="display:inline-block"></span><br></span><span class="token-line" style="color:#393A34"><span class="token plain"></span><span class="token comment" style="color:#999988;font-style:italic">// Expect</span><span class="token plain"></span><br></span><span class="token-line" style="color:#393A34"><span class="token plain"></span><span class="token function" style="color:#d73a49">expect</span><span class="token punctuation" style="color:#393A34">(</span><span class="token plain">foo</span><span class="token punctuation" style="color:#393A34">)</span><span class="token punctuation" style="color:#393A34">.</span><span class="token property-access">to</span><span class="token punctuation" style="color:#393A34">.</span><span class="token property-access">be</span><span class="token punctuation" style="color:#393A34">.</span><span class="token method function property-access" style="color:#d73a49">a</span><span class="token punctuation" style="color:#393A34">(</span><span class="token string" style="color:#e3116c">"string"</span><span class="token punctuation" style="color:#393A34">)</span><span class="token punctuation" style="color:#393A34">;</span><span class="token plain"></span><br></span><span class="token-line" style="color:#393A34"><span class="token plain"></span><span class="token function" style="color:#d73a49">expect</span><span class="token punctuation" style="color:#393A34">(</span><span class="token plain">foo</span><span class="token punctuation" style="color:#393A34">)</span><span class="token punctuation" style="color:#393A34">.</span><span class="token property-access">to</span><span class="token punctuation" style="color:#393A34">.</span><span class="token method function property-access" style="color:#d73a49">equal</span><span class="token punctuation" style="color:#393A34">(</span><span class="token string" style="color:#e3116c">"bar"</span><span class="token punctuation" style="color:#393A34">)</span><span class="token punctuation" style="color:#393A34">;</span><span class="token plain"></span><br></span><span class="token-line" style="color:#393A34"><span class="token plain"></span><span class="token function" style="color:#d73a49">expect</span><span class="token punctuation" style="color:#393A34">(</span><span class="token plain">foo</span><span class="token punctuation" style="color:#393A34">)</span><span class="token punctuation" style="color:#393A34">.</span><span class="token property-access">to</span><span class="token punctuation" style="color:#393A34">.</span><span class="token property-access">have</span><span class="token punctuation" style="color:#393A34">.</span><span class="token method function property-access" style="color:#d73a49">lengthOf</span><span class="token punctuation" style="color:#393A34">(</span><span class="token number" style="color:#36acaa">3</span><span class="token punctuation" style="color:#393A34">)</span><span class="token punctuation" style="color:#393A34">;</span><span class="token plain"></span><br></span><span class="token-line" style="color:#393A34"><span class="token plain"></span><span class="token function" style="color:#d73a49">expect</span><span class="token punctuation" style="color:#393A34">(</span><span class="token plain">tea</span><span class="token punctuation" style="color:#393A34">)</span><span class="token punctuation" style="color:#393A34">.</span><span class="token property-access">to</span><span class="token punctuation" style="color:#393A34">.</span><span class="token property-access">have</span><span class="token punctuation" style="color:#393A34">.</span><span class="token method function property-access" style="color:#d73a49">property</span><span class="token punctuation" style="color:#393A34">(</span><span class="token string" style="color:#e3116c">"flavors"</span><span class="token punctuation" style="color:#393A34">)</span><span class="token punctuation" style="color:#393A34">.</span><span class="token property-access">with</span><span class="token punctuation" style="color:#393A34">.</span><span class="token method function property-access" style="color:#d73a49">lengthOf</span><span class="token punctuation" style="color:#393A34">(</span><span class="token number" style="color:#36acaa">3</span><span class="token punctuation" style="color:#393A34">)</span><span class="token punctuation" style="color:#393A34">;</span><span class="token plain"></span><br></span><span class="token-line" style="color:#393A34"><span class="token plain" style="display:inline-block"></span><br></span><span class="token-line" style="color:#393A34"><span class="token plain"></span><span class="token comment" style="color:#999988;font-style:italic">// Should</span><span class="token plain"></span><br></span><span class="token-line" style="color:#393A34"><span class="token plain">foo</span><span class="token punctuation" style="color:#393A34">.</span><span class="token property-access">should</span><span class="token punctuation" style="color:#393A34">.</span><span class="token property-access">be</span><span class="token punctuation" style="color:#393A34">.</span><span class="token method function property-access" style="color:#d73a49">a</span><span class="token punctuation" style="color:#393A34">(</span><span class="token string" style="color:#e3116c">"string"</span><span class="token punctuation" style="color:#393A34">)</span><span class="token punctuation" style="color:#393A34">;</span><span class="token plain"></span><br></span><span class="token-line" style="color:#393A34"><span class="token plain">foo</span><span class="token punctuation" style="color:#393A34">.</span><span class="token property-access">should</span><span class="token punctuation" style="color:#393A34">.</span><span class="token method function property-access" style="color:#d73a49">equal</span><span class="token punctuation" style="color:#393A34">(</span><span class="token string" style="color:#e3116c">"bar"</span><span class="token punctuation" style="color:#393A34">)</span><span class="token punctuation" style="color:#393A34">;</span><span class="token plain"></span><br></span><span class="token-line" style="color:#393A34"><span class="token plain">foo</span><span class="token punctuation" style="color:#393A34">.</span><span class="token property-access">should</span><span class="token punctuation" style="color:#393A34">.</span><span class="token property-access">have</span><span class="token punctuation" style="color:#393A34">.</span><span class="token method function property-access" style="color:#d73a49">lengthOf</span><span class="token punctuation" style="color:#393A34">(</span><span class="token number" style="color:#36acaa">3</span><span class="token punctuation" style="color:#393A34">)</span><span class="token punctuation" style="color:#393A34">;</span><span class="token plain"></span><br></span><span class="token-line" style="color:#393A34"><span class="token plain">tea</span><span class="token punctuation" style="color:#393A34">.</span><span class="token property-access">should</span><span class="token punctuation" style="color:#393A34">.</span><span class="token property-access">have</span><span class="token punctuation" style="color:#393A34">.</span><span class="token method function property-access" style="color:#d73a49">property</span><span class="token punctuation" style="color:#393A34">(</span><span class="token string" style="color:#e3116c">"flavors"</span><span class="token punctuation" style="color:#393A34">)</span><span class="token punctuation" style="color:#393A34">.</span><span class="token property-access">with</span><span class="token punctuation" style="color:#393A34">.</span><span class="token method function property-access" style="color:#d73a49">lengthOf</span><span class="token punctuation" style="color:#393A34">(</span><span class="token number" style="color:#36acaa">3</span><span class="token punctuation" style="color:#393A34">)</span><span class="token punctuation" style="color:#393A34">;</span><br></span></code></pre><div class="buttonGroup__atx"><button type="button" aria-label="Copy code to clipboard" title="Copy" class="clean-btn"><span class="copyButtonIcons_eSgA" aria-hidden="true"><svg class="copyButtonIcon_y97N" viewBox="0 0 24 24"><path d="M19,21H8V7H19M19,5H8A2,2 0 0,0 6,7V21A2,2 0 0,0 8,23H19A2,2 0 0,0 21,21V7A2,2 0 0,0 19,5M16,1H4A2,2 0 0,0 2,3V17H4V3H16V1Z"></path></svg><svg class="copyButtonSuccessIcon_LjdS" viewBox="0 0 24 24"><path d="M21,7L9,19L3.5,13.5L4.91,12.09L9,16.17L19.59,5.59L21,7Z"></path></svg></span></button></div></div></div><p>其他拥有的测试工具：</p><ul><li>针对具体 UI 框架的测试插件，如针对 React 的 <code>@testing-library/react</code>，<code>enzyme</code>，<code>react-test-renderer</code> 等。</li><li>模拟 DOM 环境的 <code>jsdom</code>。</li><li>践行 BDD 的代表 <code>Cucumber.js</code>。</li><li>收集测试覆盖率的辅助工具 <code>istanbul</code>，或使用 v8 引擎内置的覆盖率功能的 <code>c8</code>。</li></ul><p>测试覆盖率收集原理：</p><p><code>istanbul.js</code> 提供了名为 <code>nyc</code> 的工具，执行 <code>nyc instrument <input> <output></code> 即可完成对代码的插桩。在代码实际运行时，插桩代码会统计源代码各部分的运行次数，来统计覆盖率。</p><p>例子：</p><div class="language-js codeBlockContainer_Ckt0 theme-code-block" style="--prism-color:#393A34;--prism-background-color:#f6f8fa"><div class="codeBlockTitle_Ktv7">greeting.js</div><div class="codeBlockContent_biex"><pre tabindex="0" class="prism-code language-js codeBlock_bY9V thin-scrollbar"><code class="codeBlockLines_e6Vv"><span class="token-line" style="color:#393A34"><span class="token keyword" style="color:#00009f">function</span><span class="token plain"> </span><span class="token function" style="color:#d73a49">greeting</span><span class="token punctuation" style="color:#393A34">(</span><span class="token plain">name </span><span class="token operator" style="color:#393A34">=</span><span class="token plain"> </span><span class="token string" style="color:#e3116c">"HZFE"</span><span class="token punctuation" style="color:#393A34">)</span><span class="token plain"> </span><span class="token punctuation" style="color:#393A34">{</span><span class="token plain"></span><br></span><span class="token-line" style="color:#393A34"><span class="token plain"> </span><span class="token keyword control-flow" style="color:#00009f">if</span><span class="token plain"> </span><span class="token punctuation" style="color:#393A34">(</span><span class="token constant" style="color:#36acaa">DEBUG</span><span class="token punctuation" style="color:#393A34">)</span><span class="token plain"> </span><span class="token punctuation" style="color:#393A34">{</span><span class="token plain"></span><br></span><span class="token-line" style="color:#393A34"><span class="token plain"> name </span><span class="token operator" style="color:#393A34">=</span><span class="token plain"> </span><span class="token template-string template-punctuation string" style="color:#e3116c">`</span><span class="token template-string interpolation interpolation-punctuation punctuation" style="color:#393A34">${</span><span class="token template-string interpolation">name</span><span class="token template-string interpolation interpolation-punctuation punctuation" style="color:#393A34">}</span><span class="token template-string string" style="color:#e3116c"> (DEBUG)</span><span class="token template-string template-punctuation string" style="color:#e3116c">`</span><span class="token punctuation" style="color:#393A34">;</span><span class="token plain"></span><br></span><span class="token-line" style="color:#393A34"><span class="token plain"> </span><span class="token punctuation" style="color:#393A34">}</span><span class="token plain"></span><br></span><span class="token-line" style="color:#393A34"><span class="token plain" style="display:inline-block"></span><br></span><span class="token-line" style="color:#393A34"><span class="token plain"> </span><span class="token keyword" style="color:#00009f">const</span><span class="token plain"> foo </span><span class="token operator" style="color:#393A34">=</span><span class="token plain"> </span><span class="token constant" style="color:#36acaa">DEBUG</span><span class="token plain"> </span><span class="token operator" style="color:#393A34">?</span><span class="token plain"> </span><span class="token string" style="color:#e3116c">"(DEBUG) foo"</span><span class="token plain"> </span><span class="token operator" style="color:#393A34">:</span><span class="token plain"> </span><span class="token string" style="color:#e3116c">"foo"</span><span class="token punctuation" style="color:#393A34">;</span><span class="token plain"></span><br></span><span class="token-line" style="color:#393A34"><span class="token plain" style="display:inline-block"></span><br></span><span class="token-line" style="color:#393A34"><span class="token plain"> </span><span class="token keyword control-flow" style="color:#00009f">for</span><span class="token plain"> </span><span class="token punctuation" style="color:#393A34">(</span><span class="token keyword" style="color:#00009f">const</span><span class="token plain"> i </span><span class="token operator" style="color:#393A34">=</span><span class="token plain"> </span><span class="token number" style="color:#36acaa">0</span><span class="token punctuation" style="color:#393A34">;</span><span class="token plain"> i </span><span class="token operator" style="color:#393A34"><</span><span class="token plain"> name</span><span class="token punctuation" style="color:#393A34">.</span><span class="token property-access">length</span><span class="token punctuation" style="color:#393A34">;</span><span class="token plain"> i</span><span class="token operator" style="color:#393A34">++</span><span class="token punctuation" style="color:#393A34">)</span><span class="token plain"> </span><span class="token punctuation" style="color:#393A34">{</span><span class="token plain"></span><br></span><span class="token-line" style="color:#393A34"><span class="token plain"> name </span><span class="token operator" style="color:#393A34">+=</span><span class="token plain"> </span><span class="token string" style="color:#e3116c">"!"</span><span class="token punctuation" style="color:#393A34">;</span><span class="token plain"></span><br></span><span class="token-line" style="color:#393A34"><span class="token plain"> </span><span class="token punctuation" style="color:#393A34">}</span><span class="token plain"></span><br></span><span class="token-line" style="color:#393A34"><span class="token plain" style="display:inline-block"></span><br></span><span class="token-line" style="color:#393A34"><span class="token plain"> </span><span class="token keyword control-flow" style="color:#00009f">return</span><span class="token plain"> </span><span class="token template-string template-punctuation string" style="color:#e3116c">`</span><span class="token template-string string" style="color:#e3116c">Hello </span><span class="token template-string interpolation interpolation-punctuation punctuation" style="color:#393A34">${</span><span class="token template-string interpolation">name</span><span class="token template-string interpolation interpolation-punctuation punctuation" style="color:#393A34">}</span><span class="token template-string template-punctuation string" style="color:#e3116c">`</span><span class="token punctuation" style="color:#393A34">;</span><span class="token plain"></span><br></span><span class="token-line" style="color:#393A34"><span class="token plain"></span><span class="token punctuation" style="color:#393A34">}</span><br></span></code></pre><div class="buttonGroup__atx"><button type="button" aria-label="Copy code to clipboard" title="Copy" class="clean-btn"><span class="copyButtonIcons_eSgA" aria-hidden="true"><svg class="copyButtonIcon_y97N" viewBox="0 0 24 24"><path d="M19,21H8V7H19M19,5H8A2,2 0 0,0 6,7V21A2,2 0 0,0 8,23H19A2,2 0 0,0 21,21V7A2,2 0 0,0 19,5M16,1H4A2,2 0 0,0 2,3V17H4V3H16V1Z"></path></svg><svg class="copyButtonSuccessIcon_LjdS" viewBox="0 0 24 24"><path d="M21,7L9,19L3.5,13.5L4.91,12.09L9,16.17L19.59,5.59L21,7Z"></path></svg></span></button></div></div></div><p>经过 <code>nyc instrument</code> 后，大致代码如下：</p><div class="language-js codeBlockContainer_Ckt0 theme-code-block" style="--prism-color:#393A34;--prism-background-color:#f6f8fa"><div class="codeBlockTitle_Ktv7">output.js</div><div class="codeBlockContent_biex"><pre tabindex="0" class="prism-code language-js codeBlock_bY9V thin-scrollbar"><code class="codeBlockLines_e6Vv"><span class="token-line" style="color:#393A34"><span class="token keyword" style="color:#00009f">function</span><span class="token plain"> </span><span class="token function" style="color:#d73a49">cov_g4lly5ec</span><span class="token punctuation" style="color:#393A34">(</span><span class="token punctuation" style="color:#393A34">)</span><span class="token plain"> </span><span class="token punctuation" style="color:#393A34">{</span><span class="token plain"></span><br></span><span class="token-line" style="color:#393A34"><span class="token plain"> </span><span class="token comment" style="color:#999988;font-style:italic">// ...</span><span class="token plain"></span><br></span><span class="token-line" style="color:#393A34"><span class="token plain"> </span><span class="token keyword" style="color:#00009f">var</span><span class="token plain"> coverageData </span><span class="token operator" style="color:#393A34">=</span><span class="token plain"> </span><span class="token punctuation" style="color:#393A34">{</span><span class="token plain"></span><br></span><span class="token-line" style="color:#393A34"><span class="token plain"> </span><span class="token literal-property property" style="color:#36acaa">path</span><span class="token operator" style="color:#393A34">:</span><span class="token plain"> </span><span class="token string" style="color:#e3116c">"..."</span><span class="token punctuation" style="color:#393A34">,</span><span class="token plain"></span><br></span><span class="token-line" style="color:#393A34"><span class="token plain"> </span><span class="token literal-property property" style="color:#36acaa">statementMap</span><span class="token operator" style="color:#393A34">:</span><span class="token plain"> </span><span class="token punctuation" style="color:#393A34">{</span><span class="token plain"></span><br></span><span class="token-line" style="color:#393A34"><span class="token plain"> </span><span class="token number" style="color:#36acaa">0</span><span class="token operator" style="color:#393A34">:</span><span class="token plain"> </span><span class="token punctuation" style="color:#393A34">{</span><span class="token plain"> </span><span class="token literal-property property" style="color:#36acaa">start</span><span class="token operator" style="color:#393A34">:</span><span class="token plain"> </span><span class="token punctuation" style="color:#393A34">{</span><span class="token plain"> </span><span class="token literal-property property" style="color:#36acaa">line</span><span class="token operator" style="color:#393A34">:</span><span class="token plain"> </span><span class="token number" style="color:#36acaa">2</span><span class="token punctuation" style="color:#393A34">,</span><span class="token plain"> </span><span class="token literal-property property" style="color:#36acaa">column</span><span class="token operator" style="color:#393A34">:</span><span class="token plain"> </span><span class="token number" style="color:#36acaa">2</span><span class="token plain"> </span><span class="token punctuation" style="color:#393A34">}</span><span class="token punctuation" style="color:#393A34">,</span><span class="token plain"> </span><span class="token literal-property property" style="color:#36acaa">end</span><span class="token operator" style="color:#393A34">:</span><span class="token plain"> </span><span class="token punctuation" style="color:#393A34">{</span><span class="token plain"> </span><span class="token literal-property property" style="color:#36acaa">line</span><span class="token operator" style="color:#393A34">:</span><span class="token plain"> </span><span class="token number" style="color:#36acaa">4</span><span class="token punctuation" style="color:#393A34">,</span><span class="token plain"> </span><span class="token literal-property property" style="color:#36acaa">column</span><span class="token operator" style="color:#393A34">:</span><span class="token plain"> </span><span class="token number" style="color:#36acaa">3</span><span class="token plain"> </span><span class="token punctuation" style="color:#393A34">}</span><span class="token plain"> </span><span class="token punctuation" style="color:#393A34">}</span><span class="token punctuation" style="color:#393A34">,</span><span class="token plain"></span><br></span><span class="token-line" style="color:#393A34"><span class="token plain"> </span><span class="token comment" style="color:#999988;font-style:italic">// ...</span><span class="token plain"></span><br></span><span class="token-line" style="color:#393A34"><span class="token plain"> </span><span class="token punctuation" style="color:#393A34">}</span><span class="token punctuation" style="color:#393A34">,</span><span class="token plain"></span><br></span><span class="token-line" style="color:#393A34"><span class="token plain"> </span><span class="token literal-property property" style="color:#36acaa">fnMap</span><span class="token operator" style="color:#393A34">:</span><span class="token plain"> </span><span class="token punctuation" style="color:#393A34">{</span><span class="token plain"></span><br></span><span class="token-line" style="color:#393A34"><span class="token plain"> </span><span class="token number" style="color:#36acaa">0</span><span class="token operator" style="color:#393A34">:</span><span class="token plain"> </span><span class="token punctuation" style="color:#393A34">{</span><span class="token plain"></span><br></span><span class="token-line" style="color:#393A34"><span class="token plain"> </span><span class="token literal-property property" style="color:#36acaa">name</span><span class="token operator" style="color:#393A34">:</span><span class="token plain"> </span><span class="token string" style="color:#e3116c">"greeting"</span><span class="token punctuation" style="color:#393A34">,</span><span class="token plain"></span><br></span><span class="token-line" style="color:#393A34"><span class="token plain"> </span><span class="token literal-property property" style="color:#36acaa">decl</span><span class="token operator" style="color:#393A34">:</span><span class="token plain"> </span><span class="token punctuation" style="color:#393A34">{</span><span class="token plain"> </span><span class="token literal-property property" style="color:#36acaa">start</span><span class="token operator" style="color:#393A34">:</span><span class="token plain"> </span><span class="token punctuation" style="color:#393A34">{</span><span class="token plain"> </span><span class="token literal-property property" style="color:#36acaa">line</span><span class="token operator" style="color:#393A34">:</span><span class="token plain"> </span><span class="token number" style="color:#36acaa">1</span><span class="token punctuation" style="color:#393A34">,</span><span class="token plain"> </span><span class="token literal-property property" style="color:#36acaa">column</span><span class="token operator" style="color:#393A34">:</span><span class="token plain"> </span><span class="token number" style="color:#36acaa">9</span><span class="token plain"> </span><span class="token punctuation" style="color:#393A34">}</span><span class="token punctuation" style="color:#393A34">,</span><span class="token plain"> </span><span class="token literal-property property" style="color:#36acaa">end</span><span class="token operator" style="color:#393A34">:</span><span class="token plain"> </span><span class="token punctuation" style="color:#393A34">{</span><span class="token plain"> </span><span class="token literal-property property" style="color:#36acaa">line</span><span class="token operator" style="color:#393A34">:</span><span class="token plain"> </span><span class="token number" style="color:#36acaa">1</span><span class="token punctuation" style="color:#393A34">,</span><span class="token plain"> </span><span class="token literal-property property" style="color:#36acaa">column</span><span class="token operator" style="color:#393A34">:</span><span class="token plain"> </span><span class="token number" style="color:#36acaa">17</span><span class="token plain"> </span><span class="token punctuation" style="color:#393A34">}</span><span class="token plain"> </span><span class="token punctuation" style="color:#393A34">}</span><span class="token punctuation" style="color:#393A34">,</span><span class="token plain"></span><br></span><span class="token-line" style="color:#393A34"><span class="token plain"> </span><span class="token literal-property property" style="color:#36acaa">loc</span><span class="token operator" style="color:#393A34">:</span><span class="token plain"> </span><span class="token punctuation" style="color:#393A34">{</span><span class="token plain"> </span><span class="token literal-property property" style="color:#36acaa">start</span><span class="token operator" style="color:#393A34">:</span><span class="token plain"> </span><span class="token punctuation" style="color:#393A34">{</span><span class="token plain"> </span><span class="token literal-property property" style="color:#36acaa">line</span><span class="token operator" style="color:#393A34">:</span><span class="token plain"> </span><span class="token number" style="color:#36acaa">1</span><span class="token punctuation" style="color:#393A34">,</span><span class="token plain"> </span><span class="token literal-property property" style="color:#36acaa">column</span><span class="token operator" style="color:#393A34">:</span><span class="token plain"> </span><span class="token number" style="color:#36acaa">33</span><span class="token plain"> </span><span class="token punctuation" style="color:#393A34">}</span><span class="token punctuation" style="color:#393A34">,</span><span class="token plain"> </span><span class="token literal-property property" style="color:#36acaa">end</span><span class="token operator" style="color:#393A34">:</span><span class="token plain"> </span><span class="token punctuation" style="color:#393A34">{</span><span class="token plain"> </span><span class="token literal-property property" style="color:#36acaa">line</span><span class="token operator" style="color:#393A34">:</span><span class="token plain"> </span><span class="token number" style="color:#36acaa">13</span><span class="token punctuation" style="color:#393A34">,</span><span class="token plain"> </span><span class="token literal-property property" style="color:#36acaa">column</span><span class="token operator" style="color:#393A34">:</span><span class="token plain"> </span><span class="token number" style="color:#36acaa">1</span><span class="token plain"> </span><span class="token punctuation" style="color:#393A34">}</span><span class="token plain"> </span><span class="token punctuation" style="color:#393A34">}</span><span class="token punctuation" style="color:#393A34">,</span><span class="token plain"></span><br></span><span class="token-line" style="color:#393A34"><span class="token plain"> </span><span class="token literal-property property" style="color:#36acaa">line</span><span class="token operator" style="color:#393A34">:</span><span class="token plain"> </span><span class="token number" style="color:#36acaa">1</span><span class="token punctuation" style="color:#393A34">,</span><span class="token plain"></span><br></span><span class="token-line" style="color:#393A34"><span class="token plain"> </span><span class="token punctuation" style="color:#393A34">}</span><span class="token punctuation" style="color:#393A34">,</span><span class="token plain"></span><br></span><span class="token-line" style="color:#393A34"><span class="token plain"> </span><span class="token punctuation" style="color:#393A34">}</span><span class="token punctuation" style="color:#393A34">,</span><span class="token plain"></span><br></span><span class="token-line" style="color:#393A34"><span class="token plain"> </span><span class="token literal-property property" style="color:#36acaa">branchMap</span><span class="token operator" style="color:#393A34">:</span><span class="token plain"> </span><span class="token punctuation" style="color:#393A34">{</span><span class="token plain"></span><br></span><span class="token-line" style="color:#393A34"><span class="token plain"> </span><span class="token number" style="color:#36acaa">0</span><span class="token operator" style="color:#393A34">:</span><span class="token plain"> </span><span class="token punctuation" style="color:#393A34">{</span><span class="token plain"></span><br></span><span class="token-line" style="color:#393A34"><span class="token plain"> </span><span class="token literal-property property" style="color:#36acaa">loc</span><span class="token operator" style="color:#393A34">:</span><span class="token plain"> </span><span class="token punctuation" style="color:#393A34">{</span><span class="token plain"> </span><span class="token literal-property property" style="color:#36acaa">start</span><span class="token operator" style="color:#393A34">:</span><span class="token plain"> </span><span class="token punctuation" style="color:#393A34">{</span><span class="token plain"> </span><span class="token literal-property property" style="color:#36acaa">line</span><span class="token operator" style="color:#393A34">:</span><span class="token plain"> </span><span class="token number" style="color:#36acaa">1</span><span class="token punctuation" style="color:#393A34">,</span><span class="token plain"> </span><span class="token literal-property property" style="color:#36acaa">column</span><span class="token operator" style="color:#393A34">:</span><span class="token plain"> </span><span class="token number" style="color:#36acaa">18</span><span class="token plain"> </span><span class="token punctuation" style="color:#393A34">}</span><span class="token punctuation" style="color:#393A34">,</span><span class="token plain"> </span><span class="token literal-property property" style="color:#36acaa">end</span><span class="token operator" style="color:#393A34">:</span><span class="token plain"> </span><span class="token punctuation" style="color:#393A34">{</span><span class="token plain"> </span><span class="token literal-property property" style="color:#36acaa">line</span><span class="token operator" style="color:#393A34">:</span><span class="token plain"> </span><span class="token number" style="color:#36acaa">1</span><span class="token punctuation" style="color:#393A34">,</span><span class="token plain"> </span><span class="token literal-property property" style="color:#36acaa">column</span><span class="token operator" style="color:#393A34">:</span><span class="token plain"> </span><span class="token number" style="color:#36acaa">31</span><span class="token plain"> </span><span class="token punctuation" style="color:#393A34">}</span><span class="token plain"> </span><span class="token punctuation" style="color:#393A34">}</span><span class="token punctuation" style="color:#393A34">,</span><span class="token plain"></span><br></span><span class="token-line" style="color:#393A34"><span class="token plain"> </span><span class="token literal-property property" style="color:#36acaa">type</span><span class="token operator" style="color:#393A34">:</span><span class="token plain"> </span><span class="token string" style="color:#e3116c">"default-arg"</span><span class="token punctuation" style="color:#393A34">,</span><span class="token plain"></span><br></span><span class="token-line" style="color:#393A34"><span class="token plain"> </span><span class="token literal-property property" style="color:#36acaa">locations</span><span class="token operator" style="color:#393A34">:</span><span class="token plain"> </span><span class="token punctuation" style="color:#393A34">[</span><span class="token plain"></span><br></span><span class="token-line" style="color:#393A34"><span class="token plain"> </span><span class="token punctuation" style="color:#393A34">{</span><span class="token plain"> </span><span class="token literal-property property" style="color:#36acaa">start</span><span class="token operator" style="color:#393A34">:</span><span class="token plain"> </span><span class="token punctuation" style="color:#393A34">{</span><span class="token plain"> </span><span class="token literal-property property" style="color:#36acaa">line</span><span class="token operator" style="color:#393A34">:</span><span class="token plain"> </span><span class="token number" style="color:#36acaa">1</span><span class="token punctuation" style="color:#393A34">,</span><span class="token plain"> </span><span class="token literal-property property" style="color:#36acaa">column</span><span class="token operator" style="color:#393A34">:</span><span class="token plain"> </span><span class="token number" style="color:#36acaa">25</span><span class="token plain"> </span><span class="token punctuation" style="color:#393A34">}</span><span class="token punctuation" style="color:#393A34">,</span><span class="token plain"> </span><span class="token literal-property property" style="color:#36acaa">end</span><span class="token operator" style="color:#393A34">:</span><span class="token plain"> </span><span class="token punctuation" style="color:#393A34">{</span><span class="token plain"> </span><span class="token literal-property property" style="color:#36acaa">line</span><span class="token operator" style="color:#393A34">:</span><span class="token plain"> </span><span class="token number" style="color:#36acaa">1</span><span class="token punctuation" style="color:#393A34">,</span><span class="token plain"> </span><span class="token literal-property property" style="color:#36acaa">column</span><span class="token operator" style="color:#393A34">:</span><span class="token plain"> </span><span class="token number" style="color:#36acaa">31</span><span class="token plain"> </span><span class="token punctuation" style="color:#393A34">}</span><span class="token plain"> </span><span class="token punctuation" style="color:#393A34">}</span><span class="token punctuation" style="color:#393A34">,</span><span class="token plain"></span><br></span><span class="token-line" style="color:#393A34"><span class="token plain"> </span><span class="token punctuation" style="color:#393A34">]</span><span class="token punctuation" style="color:#393A34">,</span><span class="token plain"></span><br></span><span class="token-line" style="color:#393A34"><span class="token plain"> </span><span class="token literal-property property" style="color:#36acaa">line</span><span class="token operator" style="color:#393A34">:</span><span class="token plain"> </span><span class="token number" style="color:#36acaa">1</span><span class="token punctuation" style="color:#393A34">,</span><span class="token plain"></span><br></span><span class="token-line" style="color:#393A34"><span class="token plain"> </span><span class="token punctuation" style="color:#393A34">}</span><span class="token punctuation" style="color:#393A34">,</span><span class="token plain"></span><br></span><span class="token-line" style="color:#393A34"><span class="token plain"> </span><span class="token comment" style="color:#999988;font-style:italic">// ...</span><span class="token plain"></span><br></span><span class="token-line" style="color:#393A34"><span class="token plain"> </span><span class="token punctuation" style="color:#393A34">}</span><span class="token punctuation" style="color:#393A34">,</span><span class="token plain"></span><br></span><span class="token-line" style="color:#393A34"><span class="token plain"> </span><span class="token literal-property property" style="color:#36acaa">s</span><span class="token operator" style="color:#393A34">:</span><span class="token plain"> </span><span class="token punctuation" style="color:#393A34">{</span><span class="token plain"> </span><span class="token number" style="color:#36acaa">0</span><span class="token operator" style="color:#393A34">:</span><span class="token plain"> </span><span class="token number" style="color:#36acaa">0</span><span class="token punctuation" style="color:#393A34">,</span><span class="token plain"> </span><span class="token number" style="color:#36acaa">1</span><span class="token operator" style="color:#393A34">:</span><span class="token plain"> </span><span class="token number" style="color:#36acaa">0</span><span class="token punctuation" style="color:#393A34">,</span><span class="token plain"> </span><span class="token number" style="color:#36acaa">2</span><span class="token operator" style="color:#393A34">:</span><span class="token plain"> </span><span class="token number" style="color:#36acaa">0</span><span class="token punctuation" style="color:#393A34">,</span><span class="token plain"> </span><span class="token number" style="color:#36acaa">3</span><span class="token operator" style="color:#393A34">:</span><span class="token plain"> </span><span class="token number" style="color:#36acaa">0</span><span class="token punctuation" style="color:#393A34">,</span><span class="token plain"> </span><span class="token number" style="color:#36acaa">4</span><span class="token operator" style="color:#393A34">:</span><span class="token plain"> </span><span class="token number" style="color:#36acaa">0</span><span class="token punctuation" style="color:#393A34">,</span><span class="token plain"> </span><span class="token number" style="color:#36acaa">5</span><span class="token operator" style="color:#393A34">:</span><span class="token plain"> </span><span class="token number" style="color:#36acaa">0</span><span class="token punctuation" style="color:#393A34">,</span><span class="token plain"> </span><span class="token number" style="color:#36acaa">6</span><span class="token operator" style="color:#393A34">:</span><span class="token plain"> </span><span class="token number" style="color:#36acaa">0</span><span class="token plain"> </span><span class="token punctuation" style="color:#393A34">}</span><span class="token punctuation" style="color:#393A34">,</span><span class="token plain"></span><br></span><span class="token-line" style="color:#393A34"><span class="token plain"> </span><span class="token literal-property property" style="color:#36acaa">f</span><span class="token operator" style="color:#393A34">:</span><span class="token plain"> </span><span class="token punctuation" style="color:#393A34">{</span><span class="token plain"> </span><span class="token number" style="color:#36acaa">0</span><span class="token operator" style="color:#393A34">:</span><span class="token plain"> </span><span class="token number" style="color:#36acaa">0</span><span class="token plain"> </span><span class="token punctuation" style="color:#393A34">}</span><span class="token punctuation" style="color:#393A34">,</span><span class="token plain"></span><br></span><span class="token-line" style="color:#393A34"><span class="token plain"> </span><span class="token literal-property property" style="color:#36acaa">b</span><span class="token operator" style="color:#393A34">:</span><span class="token plain"> </span><span class="token punctuation" style="color:#393A34">{</span><span class="token plain"> </span><span class="token number" style="color:#36acaa">0</span><span class="token operator" style="color:#393A34">:</span><span class="token plain"> </span><span class="token punctuation" style="color:#393A34">[</span><span class="token number" style="color:#36acaa">0</span><span class="token punctuation" style="color:#393A34">]</span><span class="token punctuation" style="color:#393A34">,</span><span class="token plain"> </span><span class="token number" style="color:#36acaa">1</span><span class="token operator" style="color:#393A34">:</span><span class="token plain"> </span><span class="token punctuation" style="color:#393A34">[</span><span class="token number" style="color:#36acaa">0</span><span class="token punctuation" style="color:#393A34">,</span><span class="token plain"> </span><span class="token number" style="color:#36acaa">0</span><span class="token punctuation" style="color:#393A34">]</span><span class="token punctuation" style="color:#393A34">,</span><span class="token plain"> </span><span class="token number" style="color:#36acaa">2</span><span class="token operator" style="color:#393A34">:</span><span class="token plain"> </span><span class="token punctuation" style="color:#393A34">[</span><span class="token number" style="color:#36acaa">0</span><span class="token punctuation" style="color:#393A34">,</span><span class="token plain"> </span><span class="token number" style="color:#36acaa">0</span><span class="token punctuation" style="color:#393A34">]</span><span class="token plain"> </span><span class="token punctuation" style="color:#393A34">}</span><span class="token punctuation" style="color:#393A34">,</span><span class="token plain"></span><br></span><span class="token-line" style="color:#393A34"><span class="token plain"> </span><span class="token comment" style="color:#999988;font-style:italic">// ...</span><span class="token plain"></span><br></span><span class="token-line" style="color:#393A34"><span class="token plain"> </span><span class="token punctuation" style="color:#393A34">}</span><span class="token punctuation" style="color:#393A34">;</span><span class="token plain"></span><br></span><span class="token-line" style="color:#393A34"><span class="token plain"> </span><span class="token comment" style="color:#999988;font-style:italic">// ...</span><span class="token plain"></span><br></span><span class="token-line" style="color:#393A34"><span class="token plain"> </span><span class="token keyword control-flow" style="color:#00009f">return</span><span class="token plain"> actualCoverage</span><span class="token punctuation" style="color:#393A34">;</span><span class="token plain"></span><br></span><span class="token-line" style="color:#393A34"><span class="token plain"></span><span class="token punctuation" style="color:#393A34">}</span><span class="token plain"></span><br></span><span class="token-line" style="color:#393A34"><span class="token plain"></span><span class="token function" style="color:#d73a49">cov_g4lly5ec</span><span class="token punctuation" style="color:#393A34">(</span><span class="token punctuation" style="color:#393A34">)</span><span class="token punctuation" style="color:#393A34">;</span><span class="token plain"></span><br></span><span class="token-line" style="color:#393A34"><span class="token plain"></span><span class="token keyword" style="color:#00009f">function</span><span class="token plain"> </span><span class="token function" style="color:#d73a49">greeting</span><span class="token punctuation" style="color:#393A34">(</span><span class="token plain">name </span><span class="token operator" style="color:#393A34">=</span><span class="token plain"> </span><span class="token punctuation" style="color:#393A34">(</span><span class="token function" style="color:#d73a49">cov_g4lly5ec</span><span class="token punctuation" style="color:#393A34">(</span><span class="token punctuation" style="color:#393A34">)</span><span class="token punctuation" style="color:#393A34">.</span><span class="token property-access">b</span><span class="token punctuation" style="color:#393A34">[</span><span class="token number" style="color:#36acaa">0</span><span class="token punctuation" style="color:#393A34">]</span><span class="token punctuation" style="color:#393A34">[</span><span class="token number" style="color:#36acaa">0</span><span class="token punctuation" style="color:#393A34">]</span><span class="token operator" style="color:#393A34">++</span><span class="token punctuation" style="color:#393A34">,</span><span class="token plain"> </span><span class="token string" style="color:#e3116c">"HZFE"</span><span class="token punctuation" style="color:#393A34">)</span><span class="token punctuation" style="color:#393A34">)</span><span class="token plain"> </span><span class="token punctuation" style="color:#393A34">{</span><span class="token plain"></span><br></span><span class="token-line" style="color:#393A34"><span class="token plain"> </span><span class="token function" style="color:#d73a49">cov_g4lly5ec</span><span class="token punctuation" style="color:#393A34">(</span><span class="token punctuation" style="color:#393A34">)</span><span class="token punctuation" style="color:#393A34">.</span><span class="token property-access">f</span><span class="token punctuation" style="color:#393A34">[</span><span class="token number" style="color:#36acaa">0</span><span class="token punctuation" style="color:#393A34">]</span><span class="token operator" style="color:#393A34">++</span><span class="token punctuation" style="color:#393A34">;</span><span class="token plain"></span><br></span><span class="token-line" style="color:#393A34"><span class="token plain"> </span><span class="token function" style="color:#d73a49">cov_g4lly5ec</span><span class="token punctuation" style="color:#393A34">(</span><span class="token punctuation" style="color:#393A34">)</span><span class="token punctuation" style="color:#393A34">.</span><span class="token property-access">s</span><span class="token punctuation" style="color:#393A34">[</span><span class="token number" style="color:#36acaa">0</span><span class="token punctuation" style="color:#393A34">]</span><span class="token operator" style="color:#393A34">++</span><span class="token punctuation" style="color:#393A34">;</span><span class="token plain"></span><br></span><span class="token-line" style="color:#393A34"><span class="token plain"> </span><span class="token keyword control-flow" style="color:#00009f">if</span><span class="token plain"> </span><span class="token punctuation" style="color:#393A34">(</span><span class="token constant" style="color:#36acaa">DEBUG</span><span class="token punctuation" style="color:#393A34">)</span><span class="token plain"> </span><span class="token punctuation" style="color:#393A34">{</span><span class="token plain"></span><br></span><span class="token-line" style="color:#393A34"><span class="token plain"> </span><span class="token function" style="color:#d73a49">cov_g4lly5ec</span><span class="token punctuation" style="color:#393A34">(</span><span class="token punctuation" style="color:#393A34">)</span><span class="token punctuation" style="color:#393A34">.</span><span class="token property-access">b</span><span class="token punctuation" style="color:#393A34">[</span><span class="token number" style="color:#36acaa">1</span><span class="token punctuation" style="color:#393A34">]</span><span class="token punctuation" style="color:#393A34">[</span><span class="token number" style="color:#36acaa">0</span><span class="token punctuation" style="color:#393A34">]</span><span class="token operator" style="color:#393A34">++</span><span class="token punctuation" style="color:#393A34">;</span><span class="token plain"></span><br></span><span class="token-line" style="color:#393A34"><span class="token plain"> </span><span class="token function" style="color:#d73a49">cov_g4lly5ec</span><span class="token punctuation" style="color:#393A34">(</span><span class="token punctuation" style="color:#393A34">)</span><span class="token punctuation" style="color:#393A34">.</span><span class="token property-access">s</span><span class="token punctuation" style="color:#393A34">[</span><span class="token number" style="color:#36acaa">1</span><span class="token punctuation" style="color:#393A34">]</span><span class="token operator" style="color:#393A34">++</span><span class="token punctuation" style="color:#393A34">;</span><span class="token plain"></span><br></span><span class="token-line" style="color:#393A34"><span class="token plain"> name </span><span class="token operator" style="color:#393A34">=</span><span class="token plain"> </span><span class="token template-string template-punctuation string" style="color:#e3116c">`</span><span class="token template-string interpolation interpolation-punctuation punctuation" style="color:#393A34">${</span><span class="token template-string interpolation">name</span><span class="token template-string interpolation interpolation-punctuation punctuation" style="color:#393A34">}</span><span class="token template-string string" style="color:#e3116c"> (DEBUG)</span><span class="token template-string template-punctuation string" style="color:#e3116c">`</span><span class="token punctuation" style="color:#393A34">;</span><span class="token plain"></span><br></span><span class="token-line" style="color:#393A34"><span class="token plain"> </span><span class="token punctuation" style="color:#393A34">}</span><span class="token plain"> </span><span class="token keyword control-flow" style="color:#00009f">else</span><span class="token plain"> </span><span class="token punctuation" style="color:#393A34">{</span><span class="token plain"></span><br></span><span class="token-line" style="color:#393A34"><span class="token plain"> </span><span class="token function" style="color:#d73a49">cov_g4lly5ec</span><span class="token punctuation" style="color:#393A34">(</span><span class="token punctuation" style="color:#393A34">)</span><span class="token punctuation" style="color:#393A34">.</span><span class="token property-access">b</span><span class="token punctuation" style="color:#393A34">[</span><span class="token number" style="color:#36acaa">1</span><span class="token punctuation" style="color:#393A34">]</span><span class="token punctuation" style="color:#393A34">[</span><span class="token number" style="color:#36acaa">1</span><span class="token punctuation" style="color:#393A34">]</span><span class="token operator" style="color:#393A34">++</span><span class="token punctuation" style="color:#393A34">;</span><span class="token plain"></span><br></span><span class="token-line" style="color:#393A34"><span class="token plain"> </span><span class="token punctuation" style="color:#393A34">}</span><span class="token plain"></span><br></span><span class="token-line" style="color:#393A34"><span class="token plain"> </span><span class="token keyword" style="color:#00009f">const</span><span class="token plain"> foo </span><span class="token operator" style="color:#393A34">=</span><span class="token plain"></span><br></span><span class="token-line" style="color:#393A34"><span class="token plain"> </span><span class="token punctuation" style="color:#393A34">(</span><span class="token function" style="color:#d73a49">cov_g4lly5ec</span><span class="token punctuation" style="color:#393A34">(</span><span class="token punctuation" style="color:#393A34">)</span><span class="token punctuation" style="color:#393A34">.</span><span class="token property-access">s</span><span class="token punctuation" style="color:#393A34">[</span><span class="token number" style="color:#36acaa">2</span><span class="token punctuation" style="color:#393A34">]</span><span class="token operator" style="color:#393A34">++</span><span class="token punctuation" style="color:#393A34">,</span><span class="token plain"></span><br></span><span class="token-line" style="color:#393A34"><span class="token plain"> </span><span class="token constant" style="color:#36acaa">DEBUG</span><span class="token plain"></span><br></span><span class="token-line" style="color:#393A34"><span class="token plain"> </span><span class="token operator" style="color:#393A34">?</span><span class="token plain"> </span><span class="token punctuation" style="color:#393A34">(</span><span class="token function" style="color:#d73a49">cov_g4lly5ec</span><span class="token punctuation" style="color:#393A34">(</span><span class="token punctuation" style="color:#393A34">)</span><span class="token punctuation" style="color:#393A34">.</span><span class="token property-access">b</span><span class="token punctuation" style="color:#393A34">[</span><span class="token number" style="color:#36acaa">2</span><span class="token punctuation" style="color:#393A34">]</span><span class="token punctuation" style="color:#393A34">[</span><span class="token number" style="color:#36acaa">0</span><span class="token punctuation" style="color:#393A34">]</span><span class="token operator" style="color:#393A34">++</span><span class="token punctuation" style="color:#393A34">,</span><span class="token plain"> </span><span class="token string" style="color:#e3116c">"(DEBUG) foo"</span><span class="token punctuation" style="color:#393A34">)</span><span class="token plain"></span><br></span><span class="token-line" style="color:#393A34"><span class="token plain"> </span><span class="token operator" style="color:#393A34">:</span><span class="token plain"> </span><span class="token punctuation" style="color:#393A34">(</span><span class="token function" style="color:#d73a49">cov_g4lly5ec</span><span class="token punctuation" style="color:#393A34">(</span><span class="token punctuation" style="color:#393A34">)</span><span class="token punctuation" style="color:#393A34">.</span><span class="token property-access">b</span><span class="token punctuation" style="color:#393A34">[</span><span class="token number" style="color:#36acaa">2</span><span class="token punctuation" style="color:#393A34">]</span><span class="token punctuation" style="color:#393A34">[</span><span class="token number" style="color:#36acaa">1</span><span class="token punctuation" style="color:#393A34">]</span><span class="token operator" style="color:#393A34">++</span><span class="token punctuation" style="color:#393A34">,</span><span class="token plain"> </span><span class="token string" style="color:#e3116c">"foo"</span><span class="token punctuation" style="color:#393A34">)</span><span class="token punctuation" style="color:#393A34">)</span><span class="token punctuation" style="color:#393A34">;</span><span class="token plain"></span><br></span><span class="token-line" style="color:#393A34"><span class="token plain"> </span><span class="token function" style="color:#d73a49">cov_g4lly5ec</span><span class="token punctuation" style="color:#393A34">(</span><span class="token punctuation" style="color:#393A34">)</span><span class="token punctuation" style="color:#393A34">.</span><span class="token property-access">s</span><span class="token punctuation" style="color:#393A34">[</span><span class="token number" style="color:#36acaa">3</span><span class="token punctuation" style="color:#393A34">]</span><span class="token operator" style="color:#393A34">++</span><span class="token punctuation" style="color:#393A34">;</span><span class="token plain"></span><br></span><span class="token-line" style="color:#393A34"><span class="token plain"> </span><span class="token keyword control-flow" style="color:#00009f">for</span><span class="token plain"> </span><span class="token punctuation" style="color:#393A34">(</span><span class="token keyword" style="color:#00009f">const</span><span class="token plain"> i </span><span class="token operator" style="color:#393A34">=</span><span class="token plain"> </span><span class="token punctuation" style="color:#393A34">(</span><span class="token function" style="color:#d73a49">cov_g4lly5ec</span><span class="token punctuation" style="color:#393A34">(</span><span class="token punctuation" style="color:#393A34">)</span><span class="token punctuation" style="color:#393A34">.</span><span class="token property-access">s</span><span class="token punctuation" style="color:#393A34">[</span><span class="token number" style="color:#36acaa">4</span><span class="token punctuation" style="color:#393A34">]</span><span class="token operator" style="color:#393A34">++</span><span class="token punctuation" style="color:#393A34">,</span><span class="token plain"> </span><span class="token number" style="color:#36acaa">0</span><span class="token punctuation" style="color:#393A34">)</span><span class="token punctuation" style="color:#393A34">;</span><span class="token plain"> i </span><span class="token operator" style="color:#393A34"><</span><span class="token plain"> name</span><span class="token punctuation" style="color:#393A34">.</span><span class="token property-access">length</span><span class="token punctuation" style="color:#393A34">;</span><span class="token plain"> i</span><span class="token operator" style="color:#393A34">++</span><span class="token punctuation" style="color:#393A34">)</span><span class="token plain"> </span><span class="token punctuation" style="color:#393A34">{</span><span class="token plain"></span><br></span><span class="token-line" style="color:#393A34"><span class="token plain"> </span><span class="token function" style="color:#d73a49">cov_g4lly5ec</span><span class="token punctuation" style="color:#393A34">(</span><span class="token punctuation" style="color:#393A34">)</span><span class="token punctuation" style="color:#393A34">.</span><span class="token property-access">s</span><span class="token punctuation" style="color:#393A34">[</span><span class="token number" style="color:#36acaa">5</span><span class="token punctuation" style="color:#393A34">]</span><span class="token operator" style="color:#393A34">++</span><span class="token punctuation" style="color:#393A34">;</span><span class="token plain"></span><br></span><span class="token-line" style="color:#393A34"><span class="token plain"> name </span><span class="token operator" style="color:#393A34">+=</span><span class="token plain"> </span><span class="token string" style="color:#e3116c">"!"</span><span class="token punctuation" style="color:#393A34">;</span><span class="token plain"></span><br></span><span class="token-line" style="color:#393A34"><span class="token plain"> </span><span class="token punctuation" style="color:#393A34">}</span><span class="token plain"></span><br></span><span class="token-line" style="color:#393A34"><span class="token plain"> </span><span class="token function" style="color:#d73a49">cov_g4lly5ec</span><span class="token punctuation" style="color:#393A34">(</span><span class="token punctuation" style="color:#393A34">)</span><span class="token punctuation" style="color:#393A34">.</span><span class="token property-access">s</span><span class="token punctuation" style="color:#393A34">[</span><span class="token number" style="color:#36acaa">6</span><span class="token punctuation" style="color:#393A34">]</span><span class="token operator" style="color:#393A34">++</span><span class="token punctuation" style="color:#393A34">;</span><span class="token plain"></span><br></span><span class="token-line" style="color:#393A34"><span class="token plain"> </span><span class="token keyword control-flow" style="color:#00009f">return</span><span class="token plain"> </span><span class="token template-string template-punctuation string" style="color:#e3116c">`</span><span class="token template-string string" style="color:#e3116c">Hello </span><span class="token template-string interpolation interpolation-punctuation punctuation" style="color:#393A34">${</span><span class="token template-string interpolation">name</span><span class="token template-string interpolation interpolation-punctuation punctuation" style="color:#393A34">}</span><span class="token template-string template-punctuation string" style="color:#e3116c">`</span><span class="token punctuation" style="color:#393A34">;</span><span class="token plain"></span><br></span><span class="token-line" style="color:#393A34"><span class="token plain"></span><span class="token punctuation" style="color:#393A34">}</span><br></span></code></pre><div class="buttonGroup__atx"><button type="button" aria-label="Copy code to clipboard" title="Copy" class="clean-btn"><span class="copyButtonIcons_eSgA" aria-hidden="true"><svg class="copyButtonIcon_y97N" viewBox="0 0 24 24"><path d="M19,21H8V7H19M19,5H8A2,2 0 0,0 6,7V21A2,2 0 0,0 8,23H19A2,2 0 0,0 21,21V7A2,2 0 0,0 19,5M16,1H4A2,2 0 0,0 2,3V17H4V3H16V1Z"></path></svg><svg class="copyButtonSuccessIcon_LjdS" viewBox="0 0 24 24"><path d="M21,7L9,19L3.5,13.5L4.91,12.09L9,16.17L19.59,5.59L21,7Z"></path></svg></span></button></div></div></div><p>istanbul 在解析源代码时，会在函数体、默认参数、分支语句等各处位置插入记录执行次数的代码，在三元运算符等特殊位置会利用 JS 逗号运算符的特性插入统计代码。</p><p>例，在<code>cov_g4lly5ec().b[1][0]++;</code> 之中的 b 代表 branch（分支），1 代表第一个分支语句，1 后面紧跟的 0 代表分支的第一个叉路。依此类推，这些代码记录了 f(function)，s(statement)，b(branch) 的执行次数。后面的索引最终会解析到 <code>statementMap</code>，<code>fnMap</code>，<code>branchMap</code> 中的对应项，映射到源代码中的具体位置。这样在执行完测试用例中，就能够知道源代码中每一处语法结构被运行的情况。</p><p><strong>E2E 测试</strong></p><p>常见工具有 Pupeteer、Nightwatch、TestCafe、Selenium、Cypress、Playwright 等。它们都是通过控制浏览器执行代码来模拟实际用户的操作，来验证 UI 的变化符合预期。E2E 测试的目的是为了尽量测试软件在真实环境下的表现，一般很少使用 mock。
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基于测试在真实的浏览器下运行，和测试环境网络不稳定两个主要因素，E2E 测试通常要执行很长的时间，并且会较频繁的面临失败。在实际的持续集成环境中，一般会让 E2E 测试重试 2 到 3 次来尽可能的排除环境因素导致的失败。</p><p>在这些常用的工具中，目前使用比较广泛的三个是 Pupeteer，Cypress，Playwright。它们三个有比较突出的特点：</p><ul><li>Pupeteer：Google 官方提供的测试工具，使用 Chrome DevTools Protocol 与 Chromium 系列的浏览器进行交互。所提供的 API 是比较底层的基本操作，通常需要自己封装常用的操作，但在具体的使用中相对灵活，限制较少。</li><li>Cypress: 高度集成的测试工具，自动等待异步操作，降低编码门槛。提供 Test Runner 可视化运行测试，记录测试步骤中的具体细节，可以查看测试代码中每一步所对应的 DOM 快照，便于 debug。基于 iframe 运行，测试代码和被测试应用处于同一运行环境，可以提高测试的可靠性。目前的限制是不支持多窗口，以及 iframe 在安全策略上的小部分无法规避的限制。</li><li>Playwright：微软开发的测试工具，支持除 Chromium 之外的 Firefox 和 Safari，拥有 Trace View 可以提供类似 Cypress 的强大 debug 体验。支持除了 JS/TS 以外的语言如 Python、.NET、Java，适用范围更广。</li></ul><p><strong>集成测试</strong></p><p>一般情况下，集成测试所需使用的工具都涵盖在单元测试和 E2E 测试使用的工具之中了。</p><h3 class="anchor anchorWithHideOnScrollNavbar_WYt5" id="进行测试的最佳实践">进行测试的最佳实践<a href="#进行测试的最佳实践" class="hash-link" aria-label="Direct link to 进行测试的最佳实践" title="Direct link to 进行测试的最佳实践"></a></h3><ol><li>测试应该足够快。只有测试能够快速运行得到反馈，测试人员才会乐意采用 TDD 的方式进行开发。反例是 E2E 测试，通常开发人员不会想要在本地频繁的运行 E2E 测试，因为这会浪费他们很多时间。使测试运行足够快，合理的配置测试框架，只运行改动相关的测试。</li><li>测试应该足够简单。如果测试代码写的非常复杂，也许会有疑问：“如何保证测试代码是正确的呢？”，那就可能需要对测试代码进行测试，所以在测试代码中，应该保证使用简单的代码，不要使用复杂、抽象度高的代码。对于确实需要使用复杂工具的场景，可以尝试使用久经考验的工具库。或者自己抽象一部分测试辅助工具代码，并对其进行测试。</li><li>测试应该具备良好的可读性。和上一条类似，保持简单的同时，也要保证良好的可读性。良好的可读性可以避免开发人员误解测试用例的意图，并可以最大限度发挥测试用例作为最佳文档的功能。虽然可读性是比较主观的感受，但也可以通过遵循下面的规则进行一定程度上的量化。<ul><li>使用 "Arrange, Act, Assert" 或 "Given, When, Then" 来组织测试代码。</li><li>每个测试块中专注于一项功能的测试，不要将太多断言混合在一起。</li><li>避免使用魔术数字和字符串，使用含义更清晰的常量取代。</li></ul></li><li>测试代码中不要重复实现源代码中的逻辑。例如，用于与实际代码返回的 Received 对比的 Expected 应该是一个简单的列举出来的字面量，而不是通过和源代码类似的逻辑动态生成的结果。</li><li>测试必须是稳定的。测试用例的成功或失败只取决于被测试的代码，测试用例不因其他用例、环境因素、外部依赖的变化而改变结果。</li><li>不要将测试与实现细节耦合。提高测试用例稳定性，避免因为代码中微小的改动而导致测试用例失败。如，使用 contain 代替 equal 检查内容；使用 getByRole 代替 querySelector。</li></ol><h2 class="anchor anchorWithHideOnScrollNavbar_WYt5" id="参考资料">参考资料<a href="#参考资料" class="hash-link" aria-label="Direct link to 参考资料" title="Direct link to 参考资料"></a></h2><ul><li><a href="https://martinfowler.com/articles/practical-test-pyramid.html" target="_blank" rel="noopener noreferrer">The Practical Test Pyramid</a></li><li><a href="http://www.jamesshore.com/v2/books/aoad1/test_driven_development" target="_blank" rel="noopener noreferrer">TDD</a></li><li><a href="https://v8.dev/blog/javascript-code-coverage" target="_blank" rel="noopener noreferrer">V8 Coverage</a></li><li><a href="https://istanbul.js.org/docs/advanced/instrument/" target="_blank" rel="noopener noreferrer">istanbul</a></li><li><a href="https://www.chaijs.com/guide/styles/" target="_blank" rel="noopener noreferrer">Assertion Styles</a></li><li><a href="https://jestjs.io/" target="_blank" rel="noopener noreferrer">Jest</a></li><li><a href="https://testing-library.com/" target="_blank" rel="noopener noreferrer">Testing Library</a></li></ul></div></article><nav class="pagination-nav docusaurus-mt-lg" aria-label="Docs pages navigation"><a class="pagination-nav__link pagination-nav__link--prev" href="/awesome-interview/book4/browser-local-storage"><div class="pagination-nav__sublabel">Previous</div><div class="pagination-nav__label">浏览器：本地存储方式及场景</div></a><a class="pagination-nav__link pagination-nav__link--next" href="/awesome-interview/book4/engineer-mfa"><div class="pagination-nav__sublabel">Next</div><div class="pagination-nav__label">工程化：谈谈微前端</div></a></nav></div></div><div class="col col--3"><div class="tableOfContents_bqdL thin-scrollbar theme-doc-toc-desktop"><ul class="table-of-contents table-of-contents__left-border"><li><a href="#相关问题" class="table-of-contents__link toc-highlight">相关问题</a></li><li><a href="#回答关键点" class="table-of-contents__link toc-highlight">回答关键点</a></li><li><a href="#知识点深入" class="table-of-contents__link toc-highlight">知识点深入</a><ul><li><a href="#测试的种类" class="table-of-contents__link toc-highlight">测试的种类</a></li><li><a href="#如何编写测试" class="table-of-contents__link toc-highlight">如何编写测试</a><ul><li><a href="#测试的结构" class="table-of-contents__link toc-highlight">测试的结构</a></li><li><a href="#测试工具" class="table-of-contents__link toc-highlight">测试工具</a></li></ul></li><li><a href="#进行测试的最佳实践" class="table-of-contents__link toc-highlight">进行测试的最佳实践</a></li></ul></li><li><a href="#参考资料" class="table-of-contents__link toc-highlight">参考资料</a></li></ul></div></div></div><div class="row"><div class="col"><div class="react-utterences"><div>Loading script...</div></div></div><div class="col col--3"></div><div class="chatbox-container" style="height:0"><div style="flex-grow:1;padding:0 10%"><iframe src="https://interview-book-ai.hzfe.org" height="100%" width="100%"></iframe></div></div></div></div></main></div></div></div>
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