I agree that you can decline to take the tests.

To answer your question, my only knowledge of autism testing is how they did it for my then-3-year-old daughter, so I'm sure it's different for adults. I mean, if you really don't want the diagnosis, you could probably opt to throw the test, like I imagine some questions should be obvious in whether they're screening for autism (like, "I have trouble reading others' emotions"). So you could answer them dishonestly, I suppose.