There are valid reasons to write code to determine if your vehicle is being tested. Modern cars contain all sorts of computerized safety features that would go

There are valid reasons to write code to determine if your vehicle is being tested. Modern cars contain all sorts of computerized safety features that would go active in the typical test scenario thereby preventing the static tests that the EPA and others do. So the car detects wheels straight, only drive wheels turning, and so on, so it disengages the features that would active traction control, reducing engine power, and more. The key here is that VW engineers went further and used that as they indicator to run the full emissions process and only then. There is no viable reason to have any toggle on emissions processes except perhaps with regards to cold weather starts.