Since Unit Testing is becomming a defacto used practice in modern programming, this is an interesting topic to say the least:

The next XP BE meeting will be hosted by Philippe De Bruycker of the
Federal Administration of Foreign Affairs in Brussels.

The topic of the evening will be "Unit Tests as documentation". If you
have something to tell about the subject, let us know. Even better, if
you have some unit tested code, why not bring it along so that we can
see if the tests (help) document your code?

More info and registration at

Because you need a badge to get in (and out), register at least a week
before the meeting. Put your first+last name and car registration number
  on the list on the wiki.