I've recently been working on a project trying to take an existing customized wordpress site and create automated integration tests around parts of it. I'm using phpUnderControl, phpUnit, Selenium RC, Firefox, Xvfb (virtual frame buffer) and...well, I think that's it.
He mentions the two issues he came across, both with the WordPress software (the "siteurl" setting and the pathing for the templates). He recommends that application code be portable to avoid problems like these. Applications that can be dropped in anywhere and "just work" can help not only make life easier for the installer but also for the tester.