Well as long as you have a prescription for testosterone, it doesn't matter what they mark on your drug test. If they mark female, and you show proof that you are supposed to be taking testosterone, I doubt that you can get in any trouble. Oh, and they don't test that sort of stuff on drug tests anyway. Women pee for men and vice versa for eachother all the time when the one whom is administered the test is on drugs. Also, as a huge corporation, walmart can get in a great deal of trouble if you are discriminated against based on your gender identity. If it comes up, be honest, and ask that your manager keeps it to his/herself due to the un-accepting nature of the individuals in your town.