Before the Hollowfication Incident (in the anime) we see Kisuke Urahara is called to a room to meet with Head Captain Genryūsai Shigekuni Yamamoto, with the presence of 2 other captains. After this, he is revealed to be the new Squad 12 Captain, so we can infer that this was the Captain's Exam.
Earlier in the series we learned that it is a requirement that all Captains had to master Bankai to become a Captain (with the exception of Kenpachi Zaraki), but I don't see how Kisuke's Bankai can be evaluated in that small room. Also given how they were seated it seemed as if all they would do is talk.
So what exactly happens during a Captain's Exam?