Already done. It's funny how the press is only talking about VW but meanwhile there are first tests showing that many other manufacturers do/did the same.
That wasn't "the same". In those cases, they optimized for the kind of environment the tests have (which regulators encourage as that test is supposed to be representative). They didn't have the computer detect whether a specific run was a test, as VW did.
http://www.theguardian.com/environment/2015/oct/09/mercedes-...