Documentations about testing

Hi,
The first of all: Thank to everybody for the mode, I've been using it for a long time.

At this moment I'm trying to learn some of emacs lisp, and I'm thinking in practice with a mode that I use, for example this one, but I have some doubts with the testing.

What is a php.face file? Exists any documentation about how to test and how you develop this mode?

Thank.

PS: I don't know how to set a "question" tag and if this is the right place to ask.