I wouldn't call it 'rigged tests', it's more like they optimize the system under test to meet the spec. It probably happens everywhere, not only in cars. The behavior of your fridge, AC or any other hardware is probably optimized in weird ways just to meet Energy Star etc.
You would do so wrongly. In these cases, like VW, the car is programmed specifically to detect when it is being tested, and lower emissions. They aren't optimizing to test spec, they are cheating. There's no other word for it.
For example, commercial compilers are often written to specifically detect and rewrite idioms/code in oft-used benchmarks (that aren't common to the real world), etc Your browser's javascript engine almost certainly does it.
They aren't cheating, they are just making the test worthless by optimizing it. They still shouldn't do it, but it's super-common.