Cheating

What are people's thoughts about what to do in a situation where you have reason to believe that a classmate is about to cheat on say, a closed-book in-class exam? (in no way is this question meant to imply that there is cuny-wide issue with cheating.)

The academic integrity policy on pages 16-19 of the handbook are of little guidance in this area. There does not seem to be a duty to report but should we? There can be some severe consequences but only after a fact-finding process.

Stay out of it?
Don't stress yourself before taking the exam?
Report?
Confront?
Something else?