Take a hint from Maarten Manders when renaming and moving around your unit testing order:

It's absolutely amazing how much you can mess up unit tests just by changing their order! (Trevi_* comes after Tilllate_*) Everyone knows that tests are supposed to be independent. But we all know how it is.

He asks for recommendations on what to do to help the situation. Comments on the post (including ones from Lukas Smith and Sebastian Bergmann) mention using PHPT, a new version of PHPUnit that will do just what he wants and whether or not to use Singletons.