Undergoing testing on the Stelvio pass - Porsche's forthcoming four-door saloon/coupe. The silhouette of the car appeared to be the real thing, but there were various bits of superficial disguise that were apparently designed to divert attention from the true window and shut lines, although these could, for the most part, still be made out. No photo, I'm afraid - just couldn't get my camera out in time. The Panamera was coming the other way and was gone in a flash, if you'll forgive the pun. Anyway, have a Google and you'll find that there are plenty of surreptitious pix of this thing out there already. I'm not sure it looked quite as nice as the Mercedes CLS or the photos I've seen of the Aston Martin Rapide - my impression was of something that was slightly dumpy at the rear, although that could have been a trick induced by the light disguise.
My guess would be that Porsche wasn't exploring or tuning the car's outright handling capabilities on the Stelvio because you can't really get up enough speed for that sort of thing on large sections of the pass. So it was probably stuff like brakes, transmission and cooling system that were being put to the test here - and how.
I also saw a Vectra on the pass that seemed to have one or two small pieces of superficial disguise at the front or rear and a deep, rumbly engine note - not sure what that was but again, it could have been a manufacturer's car undergoing testing of some minor mods, or something more exciting hiding under a plainish skin.