[plt-scheme] Using scheme-unit from DrScheme

I'm trying to get the "tests" feature of DrScheme to work (BTW, it was a
truly brilliant idea to include this).  I don't know how to do it, though,
and the SchemeUnit docs online seem geared towards writing tests as
scripts.  Hitting the "tests" button brings up a window for the tests, and
hitting "add" in that window brings up a dialog.  The dialog box says to
"enter an expression that will evaluate to a test or list of tests in the
text box".  What kind of expression is that?  Is there a tutorial for this
floating around somewhere?

Mike