Anyone using UG in a testing situation must be stupid anyway.
I dunno...
IMO, if the athlete is going to be tested, he should tell the supplier/ugl.
the last thing any ugl wants is BAD publicity, such as a fighter telling all his teammates/friends fellow fighters that he was using a certain UGL's test prop or test ace at what he believed was 100mg/day and ended up with 25mg/day of masteron enanthate and tested positive. (I can't think of anything masteron would be used in place of.. besides primobolan.. maybe he believed he was getting 50/day primo ace and actually got 50/day mast enan.. I guess that'd make more sense, and more profit for the supplier, charging primo prices for masteron cost and making 4x the profit).
likewise... if the athlete uses a certain ugl, and he gets exactly what he wanted and tests clean and gets the right drug at the right dosage, he'll in turn, tell all his teammates and generate business for the ugl, as the word would get out that he/they (the ugl) are trustworthy.