Roy Ganor explains in his blog:

Since Michael has just finished implementing the second phase for PHP 5.3 support in PDT, we can now expose unit tests and ask users to add more cases to the code assist tests repository.

His post includes the basic format for the tests (as written in pdtt, a clone of the phpt format) and a clip from the PDT wiki page about why they need them. There's no automatic way to submit them but if you want more information on the project and testing, you can always send them an email to find out more.