Top 3 javascript-testing Open-Source Projects

mockttp

18 741 8.1 TypeScript

Powerful friendly HTTP mock server & proxy library

Project mention: Client-side proxies – a better way to individualise the Internet? (2000) | news.ycombinator.com | 2023-07-23

Interesting how the world has changed since the 2000s here - nowadays the ecosystem is far better, so it's much easier to set up tools to mess around with this, but the use of HTTPS everywhere makes it more difficult in more advanced cases (e.g. you'll often need to fight certificate configuration in individual clients).
In part because of that, browser extensions have become the main way to go for this kind of local web modification, but now there's new restrictions slowly coming in there too.
If you want to mess around with HTTP-level rewriting for yourself though, I maintain a Node.js library for easily writing tiny custom HTTP & HTTPS-intercepting proxies that makes it very easy: https://github.com/httptoolkit/mockttp/. Others have built more specific tooling on top too, like this web page modification proxy: https://github.com/OnkelTem/wmod-proxy
There's a walkthrough for setting up a quick local proxy & rewriting your own browser traffic here: https://httptoolkit.com/blog/javascript-mitm-proxy-mockttp/

auto-spies

1 173 5.8 TypeScript

Create automatic spies from classes
SurveyJS

surveyjs.io featured

Open-Source JSON Form Builder to Create Dynamic Forms Right in Your App. With SurveyJS form UI libraries, you can build and style forms in a fully-integrated drag & drop form builder, render them in your JS app, and store form submission data in any backend, inc. PHP, ASP.NET Core, and Node.js.
bigtest

1 99 2.1 TypeScript

Ensure your React/Vue/Ember/anything app works perfectly across browsers.

NOTE: The open source projects on this list are ordered by number of github stars. The number of mentions indicates repo mentiontions in the last 12 Months or since we started tracking (Dec 2020).