prohormoes (considered illegal) will show up on a drug test as testosterone as that is what most of them convert to once they get into the body (5-AD's, 1,4-diols, etc...). So if your company is paying a ton of extra money to run steroid tests apart from the normal drug test you will be busted, however you can show them the pro's (if they are legal) if you test positive and it may not be that big of a deal (as long as you don't test positive for meth to). However, wooody is right in that they don't normally test for steroids in a company drug test and that the side effects can actually be worse using prohormones than gear. In my opinion the prohormones still considered legal will not show up on a piss test no matter what because they are not close enough to the real thing, however if they do you can show them the pro's and see what happens.
I want to let you know that I haven't done research into prohormones for several years now, so take everything I've said here with a grain of salt. When I was using everything was legal, but to my knowledge all of the things that gave really good gains and were similar in structure and function to steroids were banned. Hopefully someone else can either confirm what I've said or tell me I'm full of shit, which I will gladly accept. Either way we will both learn from this post. Have a good day.