Makes sense. As I said, emission testing is often not performed when the vehicle is being driven/under load. States could incorporate dyno testing, but its technical, complicated, and unsafe.
Is that what it was?
I though it was when the car is on a dyno only the drive wheels turn while the other 2 are stationary.
You are correct, the steering wheel approach is very smart... all I was suggesting was that dyno testing would limit the ability to defeat, but testing stations would also need to simulate more of the vehicles systems.