Simplifying Cross-Browser Javascript Unit Testing

Jan 18, 2012 · 2 min read

Written by Daniel Straus and Eric Garside

Javascript unit testing is complicated and expensive; unlike server-side logic, code that seems to work fine may execute differently on different browser/OS combinations, which means that in order to get adequate test coverage, all supported platforms need to be tested thoroughly. In order to allow our codebase to be testable as it grows in size we came up with a way to make our testing process easy and scalable.

To write our tests we used ScrewUnit, a behavior-driven testing framework which provides an extensible cross-browser utility for developing tests. Each test suite is just a web page; running it is only as difficult as pointing a browser at it. Let take a look at an example:

This test passes in a Webkit browser, but not in Internet Explorer (IE can’t process the date format). As you can imagine, it would be quite time consuming to have to run tests like this on multiple browsers manually on every check-in.

To make the use of ScrewUnit manageable and efficient we turned to Selenium-WebDriver (a browser automation tool). We can write Selenium routines to open a project’s ScrewUnit test and analyze its results. With a single line of code, we can check if ScrewUnit detects failures:

This is improved over the previous method. But to make this process optimal we wanted to run these routines in parallel. To accomplish this (run across multiple browser/OS combinations) we used Sauce Labs. Sauce Labs allows us kick off tests from a single machine quickly and doesn’t require a large testing hardware infrastructure on our end (everything runs in the Sauce Labs’ cloud). Below is an example of how this all comes together:

By combining ScrewUnit, Selenium and Sauce Labs, we removed the complexity of running Javascript unit tests across multiple browsers. We’ve put together a demo of our tests as they run on our own project.


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