I have a question: Why do you WANT to take the AP test? Is it because you don't want to take physics in college (it would be a general education class and you are planning on majoring in art, history, etc.), or because you want to skip a course and "surge ahead" in physics?
Note: I am personally against taking AP tests to surge ahead in your field of interest or related fields. In my day, you took AP tests to receive credit for subjects that you didn't want to major in (in my case, I received AP credit for history and English, leaving me more time so I could take almost all the upper level electives in math, physics and chemistry... even though I started my physics major a term late). I'd also personally suggest being a term ahead in the calculus sequence than where you are in the physics sequence (if you are ever interested in taking calculus-based physics).
That said: yes, I concur that you should know the material in an actual textbook of appropriate level... then use the test prep book(s) as review and practice.