Busted!

There are plenty of people throwing accusations around at athletes who "appear" to be using performance-enhancing substances to improve themselves in competition. Some of these, including seven-time Tour de France winner Lance Armstrong, can at least say they haven't failed a test.
His successor and former teammate, Floyd Landis, apparently had elevated testosterone levels in a recent test. If the numbers were outside a particular range, that would be a failed test. I don't know the actual levels, but a failed test would give new amunition to the French about American riders and create more questions about Armstrong.
After all, it could be argued Landis learned at Armstrong's hip how to win races.