ABJS is a contrib Drupal module, and, without any requirements or ties to paid services, is as low cost as you can get. As we’ll see, it’s pretty basic but it really lets you get down to building your own understanding of how A/B testing works. The beauty of ABJS is in its simplicity. The settings pages are fairly self-explanatory, which is really helpful. Let’s set up a basic A/B test to show how things work.