- Unit Testing
- Mocking
- Inversion of Control
- Refactoring
- Object Relational Mapping
- Others?
I have found simpletest for unit testing and mocking and, though it leaves much to be desired, it kind-of sort of works.
I have yet to find any reasonable Inversion of Control framework (there is one that came up on phpclasses but no documentation and doesn't seem like anyone's tried it).