Many available frameworks such as JsUnit do in-browser testing. If you want to test actual UI code, that’s obviously what you need. But we have that at least partly covered with Selenium, and a problem with these tests is that they are difficult to run in an automated way, like from our ant test task. So I wanted something to easily and quickly test the UI-independent code, along with the Java code, from the command line, ant, or scripts. I also think that a standard JUnit-style test is way easier to write, but I guess that depends on what you’re used to.