[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.
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']) }) })
【推荐】国内首个AI IDE,深度理解中文开发场景,立即下载体验Trae
【推荐】编程新体验,更懂你的AI,立即体验豆包MarsCode编程助手
【推荐】抖音旗下AI助手豆包,你的智能百科全书,全免费不限次数
【推荐】轻量又高性能的 SSH 工具 IShell:AI 加持,快人一步
· 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
· 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
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