June 2021
Intermediate to advanced
290 pages
9h 21m
Chinese
Content preview from Node与Express开发（第2版）
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40
｜
第
5
章
5.7
单元测试
现在可以把注意力转到单元测试上了。既然单元测试的重点是隔离单个函数或组件，那么
就先来学习模拟（
mocking
）
，它是实现这种隔离的重要技术。
5.7.1
模拟
如何写出“可测试”的代码是我们经常会遇到的一个挑战。一般来说，试图做太多事情或
者设想了太多依赖的代码，比起更专注、设想更少依赖或没有依赖的代码要更难于测试。
每当代码中多了一个依赖，为了保证测试的有效性，就需要多模拟一处。例如，我们主要
的依赖是
Express
，它已经经过了完整的测试
，所以不必（也不想）测试
Express
本身，只
需测试
使用它的方式
。要确定是否在正确地使用
Express
，唯一的方法是模拟
Express
本身。
目前，我们的路由（主页、“关于”页、
404
页和
500
页）是很难测试的
，因为它们设想了
3
个有关
Express
的依赖
：
Express
的
app
对象（所以才能调用
app.get
）、
request
对象以及
response
对象
。幸运的是，要消除对
app
对象的依赖十分容易（
request
和
response
对象要
难一点儿，后面会详细介绍）。而且，我们并没有使用过多来自
response
对象的功能
（只
使用了
render
方法），因此也很容易模拟，一会儿就会看到。
5.7.2
为可测试性而重构应用
我们的应用还没有太多代码可以测试。目前才只是加了几个路由处理函数和一个
getFortune
函数。
为了让应用更易于测试，我们准备把实际的路由处理函数
提取
到它们自己的库中。创建文
件
lib/handlers.js
（版本库的 ...
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I'm always learning. So when I got on to O'Reilly, I was like a kid in a candy store. There are playlists. There are answers. There's on-demand training. It's worth its weight in gold, in terms of what it allows me to do.