You ask a good but difficult question. When I was supporting someone with aspergers at their P.T. session, this very question came up. And she told me you don't really see adults going to get tested because of the stigma attached to autism and as an adult they have found a successful way to cope in society.
That was a number of years back. With no one commenting on your post, I couldn't help but recall that conversation.
Sorry I didn't really give you an answer.