TestSwarm, Distributed Continuous Integration for JavaScript
Do you believe that jQuery project is 4 years old now ? The project is even more mature with the latest TestSwarm alpha released this week, "jQuery is now being tested against 50 browsers on 9 platforms, on every commit. That's pretty much insane.", said John Resig, the creator of jQuery and TestSwarm.

TestSwarm provides distributed continuous integration testing for JavaScript. It was initially created by John Resig as a tool to support the jQuery project and has since moved to become an official Mozilla Labs project.
Actually TestSwarm is provided as a service to test few popular JavaScript libraries including jQuery, YUI, Dojo, MooTools, and Prototype. You can also download source code and setup your own swarm. TestSwarm will give you a visual interface for failed or successful tests against every single commit and different browsers, which make it really easy to locate any error and keep JavaScript libraries compatible with most web browsers.
You can see below a screencast of the TestSwarm site :











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