[Unit Testing] Mock a Node module's dependencies using Proxyquire

Sometimes when writing a unit test, you know that the module you're testing imports a module that you would like to observe, or at the very least mock to prevent side effects like network activity or file system operations.

For JavaScript unit tests that run in Node, we can hijack the built-in require function by using the proxyquire module, which allows us to mock one or more modules that are second-class dependencies in our unit test, replacing them with whatever we want.

This means we could replace functions with no-ops to prevent side effects, or replace them with Sinon spies to observe the inner workings of the module you're testing.

In this video, we'll demonstrate the basics of using Proxyquire to prevent and observe a file system operation.

 

index.js:

const fs = require('fs');

exports.writeFile = (filename, contents) => {
  fs.writeFileSync(filename, contents.trim(), 'utf8');
}

 

For unit testing, we don't want to call 'fs.writeFileSync', instead we want to using mock function.

复制代码
const assert = require('assert');
const proxyquire = require('proxyquire');
const sinon = require('sinon');

const fsMock = {};
// In index.js file, we want to mock 'fs' module with our fsMock object
const main = proxyquire('./index.js', {'fs', fsMock});
describe('main.writeFile', () => {
  it('should write a trimmed string to the specififed file', () => {
    fsMock.writeFileSync = sinon.spy();
    main.writeFile('file.txt', 'string');
    assert.deepEqual(fsMock.writeFileSync.getCall(0).args, ['file.txt', 'string', 'utf8'])
  })
})
复制代码

 

posted @   Zhentiw  阅读(394)  评论(0编辑  收藏  举报
编辑推荐:
· SQL Server 2025 AI相关能力初探
· Linux系列:如何用 C#调用 C方法造成内存泄露
· AI与.NET技术实操系列(二):开始使用ML.NET
· 记一次.NET内存居高不下排查解决与启示
· 探究高空视频全景AR技术的实现原理
阅读排行:
· 阿里最新开源QwQ-32B,效果媲美deepseek-r1满血版,部署成本又又又降低了!
· Manus重磅发布:全球首款通用AI代理技术深度解析与实战指南
· 开源Multi-agent AI智能体框架aevatar.ai,欢迎大家贡献代码
· 被坑几百块钱后,我竟然真的恢复了删除的微信聊天记录!
· AI技术革命,工作效率10个最佳AI工具
历史上的今天:
2018-01-03 [Poi] Build and Analyze Your JavaScript Bundles with Poi
2018-01-03 [Poi] Use Markdown as React Components by Adding a Webpack Loader to Poi
2018-01-03 [Poi] Build a Vue App with Poi
2018-01-03 [Poi] Customize Babel to Build a React App with Poi
2016-01-03 [ES6] Object.assign (with defaults value object)
2016-01-03 [ES6] Objects create-shorthand && Destructuring
2016-01-03 [ES6] Spread Operator
点击右上角即可分享
微信分享提示