Even if Fed does dope (or Nadal or Nole or Murray), we will never find out about it.
I mean they swept Agassi's meth use under the rug no problem.. Why wouldn't they do that to the top money makers for the sport today?? Hell we didn't even find out about Andre's drug use until his book came out. Yet the powers that be knew about it all these years.
Sports are a dirty business.. Bottom line.
They aren't going to risk losing their reputation by airing the dirty laundry of the top players.. Think about it.
It would take some legit outside investigations and state of the art drug testing, to really catch these top guys