If it's the ADOS, then I was there when my 13yo son had his a few years ago (sitting at the back of the room, not contributing - I was just there to confirm whether his behaviour during the ADOS was "normal for him.")
I was actually amazed how good the ADOS was for picking out the things he couldn't do, or approached differently. I don't remember much of it, but there were things like showing him a picture and asking him to describe it. Over and over again I found myself thinking, "well, it's no good asking him that, he doesn't think in that way." I'd been sceptical about how good a scientific test there could be for autism, but by the end I was really impressed (and also fully convinced that he would get a diagnosis, because the ADOS was clearly constructed for people like him!).
When my DD had the ADOS, she was 15 and I think did a different version. I wasn't there for it. She was nervous beforehand and I tried to persuade her that this wasn't a "test" where there were any "right" answers. She was tired afterwards and didn't discuss it much. She mentioned that the psychiatrist had asked how she saw her future, and asked why she thought people chose to get married.
Overall the professionals conducting the tests were very friendly and reassuring, and tried to put DS and DD at their ease. There was some "chat" as well as questioning, although I suspect the chat was often just a more open-ended form of assessment.
I also completed questionnaires and had appointments (without the kids) to discuss their early childhoods, in advance of the ADOS assessments.
(Incidentally, they both received diagnoses, although DD masks very well.)