I believe it depends on the regulations for a specific tank manufacturer. There are some odd type things that go along with the test perameters as well. I don't recall specifics but it had something to do with expansion limits or something along those lines.
If you pull up a PDF of a tank's special perit, it will have the testing criteria in it - which will give you the pressure used for that tank manufacturer.
EDIT: Here is a special permit for a Luxfur cylinder: http://www.phmsa.dot.gov/staticfiles...2009100578.pdf
. Read up on page 3, part b. The cylinder is to be filled to 5/3 of the marked cylinder pressure. The specifics I couldn't recall have to do with the elastic expansion (part b, ss 2.).