HTMLUnit

Maybe the best and most useful session I attended at JavaOne today was on HTMLUnit.
(TS-4238 HtmlUnit: An Efficient Approach to Testing Web Applications given by Ahmed Ashour, Zain KSA; Daniel Gredler, DHL Global Mail).
The library is hardly new, but I've never really looked at it. I think I always figured that the nasty complex struts based stuff I worked on at work didn't really suit itself to this kind of testing.

As it turns out HTMLUnit is a complete browser simulation. By complete, that includes javascript execution, among other things. You load up pages, examine DOM elements, make assertions, and all of the other sweet stuff you'd expect.

Even spiffier, you can test AJAX applications.

It also lets you work with 3rd party javascript libraries like GWT, jquery, Prototype, that let you test your html generated by the javascript. That's some serious power.