sphan,
Having worked in Flight Test for the best part of 25 years, firstly congratulations on getting an interview! Genghis has answered the technical side of your post (I suspect he's the author of one of the recommended books) but for a more general one, there should have been several links to previous threads. Unfortunately it looks like they have been purged as the links no longer work - they were fairly old.
You must have had some - possibly a lot - of experience to have obtained your interview so if this seems old hat please forgive me. From my experience inside a civilian test organization (I survived G's lay off), FTEs are recruited from within the FT Engineering organization unless they have already been one in the military and even then it may not be a slam dunk unless they have some mutual acquaintances. In short, if you are aiming for a civilian FTE position, I would apply for a job in the Flight Test group using whatever degree you have and then see what opportunities are available. Best of luck!