I have not heard of any "minimum" number of bolts to test. What I've usually seen is 2 test anchors in roadway decks just to prove that the contractor's "procedure" works. I've also seen, on the one parking structure anchor testing I was involved with, that a minimum of 10% was required by the engineer of record. Thus kind of repeating what PA had mentioned, it really is up to the engineer as to the required "minimum" number to test.
Depending on what you're doing the pull-out test for, and which state you're in, there may be some standards as to rate of loading, max load to test to, duration to hold the load, etc.
I know that around here, both RIDOT (Rhode Island DOT) and MADOT (Massachusetts DOT) have requirements, depending on loading scenario, what the max load is supposed to be, duration to hold load, etc. Both of these DOTs follow some form of ASTM E488 "Standard Test Methods for Strength of Anchors in Concrete and Masonry Elements".
I would say that as long as the ASTM is folowed somewhat, you can set your required load to whatever you feel comfortable with, for as many as it would take for you to feel confident that the anchors were installed correctly.