http://www.usna.edu/acdean/candidateinfo/USNACourseValidationPolicy.htm
Chinese is not listed for some reason, but Chinese is tested during Plebe Summer. Calc I is tested online via CABS.
In addition to this, validation can be requested on an individual basis by speaking to the chair of the department.
Validate everything you can. If you got a 5 on the AP test, definitely validate.
For example, the Chemistry final last semester was so much easier than the Chem AP test; if you crushed the Chem AP test you will waste your time taking SC111/SC112. Same with Calculus; if you crushed Calc BC, validate Calc I and II.
Sure, you could get easy As. Boost your GPA and whatnot. And I could major in Chinese as a native speaker and have the easiest four years possible. But what's the point of that? You'll open up the door to so many opportunities if you validate: study abroad, VGEP, double major, or simply taking more electives that interest you, rather than sitting through a class you've already taken and being thoroughly bored.
If you can pass the validation test, unless it was some kind of fluke, it means you can succeed at the next level and you'll probably be wasting your time if you're not placed in the next level.