Like I said, I don't know of anyone for certain, so I am not going to assume until I know for a fact they are. A few people got tested a while back, and that helped clear the air. But it isn't hard to tell if someone is doping. You can easily smell it under caution or in the pits in some cases, and I have personally seen someone leave black tire tracks on the track while we were rolling around before the race started, and lately i have neither smelt any or seen any on tires, when you are surrounded by it on a regular basis, and are on the track enough you pick up on the subtle things on competitors cars, ie tire doping, fuel additives, tire pressure estimates, tire spacing, offsets, etc.