No, Watir scripts a running instance of IE. I have code in my Watir scripts that call out to a 3rd-party tool for taking screenshots. This is how I get a gallery of images showing all the pages in the app as actually seen in IE.

I also use Selenium to script a running browser instance; I do most of the heavy UI testing with that because I can run it on Ubuntu. It's with Selenium that I interact with forms, make sure ajax calls return correct values, pages have the right content, pages aren't giving me error messages, etc.

Some of this is also doable headless, and for many things headless (or just hitting the code via bacon or something) is of course faster, but using Selenium IDE I can record my interaction with a page then edit or expand the recorded script. So it's fairly trivial to create tests.

But I rarely do it test-driven. It's mainly to ensure that while I'm changing something in one place I don't inadvertently screw up a page someplace else that I may forget to check.

I think there was one app I tried to do the HTML TDD, but I soon found that it was much better for me to sketch out page design and flow and add tests as a I went.