Super Fast JS Testing

August 12th, 2009 · 10 Comments ·

by Shyam Seshadri

Before I jump into how exactly you can perform super fast and easy JS testing, let me give you some background on the problem.

Javascript is a finicky language (Some people even hesitate to call it a language). And it can easily grow and become a horrible and complicated beast, incapable of being tamed once let loose. And testing it is a nightmare. Once you have decided on a framework (of which there are a dime a dozen), you then have to set it up to run just right. You need to set it up to actually run your tests. Then you have to figure out how to run it in a continuous integration environment. Maybe even run it in headless mode. And everyone solves it in their own ways.

But the biggest problem I have with most of these frameworks is that executing the tests usually requires a context switch. By that, I mean to run a JSUnit test, you end up usually having to open the browser, browse to a particular url or html page which then runs the test. Then you have to look at the results there, and then come back to your editor to either proceed further or fix your tests. Works, but really slows down development.

In java, all it takes is to click the run button in your IDE to run your tests. You get instant feedback, a green / red bar and details on which tests passed and failed and at what line. No context switch, you can get it to run at every save, and proceed on your merry way. Till now, this was not possible with Javascript.

But now, we have JS Test Driver. My colleagues Jeremie and Misko ended up running into some of the issues I outlined above, and decided that going along with the flow was simply unacceptable. So they created a JS Testing framework which solves these very things. You can capture any browser on any machine, and when you tell it to run tests, it will go ahead and execute them on all these browsers and return you the results in your client. And its blazing fast. I am talking milliseconds to run 100 odd tests. And you can tell it to rerun your tests at each save. All within the comforts of your IDE. And over the last three weeks, I have been working on the eclipse plugin for JS Test Driver, and its now at the point where its in a decent working condition.

The plugin in action

The plugin allows you to, from within Eclipse, start the JS Test Driver server, capture some browsers, and then run your tests. You get pretty icons telling you what browsers were captured, the state of the server, the state of the tests. It allows you to filter and show only failures, rerun your last launch configuration, even setup the paths to your browsers so you can launch it all from the safety of eclipse. And as you can see, its super fast. Some 100 odd tests in less than 10 ms. If thats not fast, I don’t know what is.

For more details on JS Test Driver, visit its Google Code website and see how you can use it in your next project and even integrate it into a continuous integration. Misko talks a little bit more about the motivations behind writing it on his Yet Another JS Testing Framework post. To try out the plugin for yourselves, go add the following update site to eclipse:

For all you IntelliJ fanatics, there is something similar in the works.

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