I have been searching for a Pocket PC version of NUnit for some time now.
Jimmy Armitage has released a solid first attempt at accomplishing this goal.
http://www.opennetcf.org/forums/topic.asp?TOPIC_ID=324
Here is one that is written in German and has baffeled me so far.
http://www.designstate.com/2003/html/bx_nunit.htm
Here is one that is written in English and also has baffeled me so far.
http://www23.brinkster.com/aewk/nunit/NUnit_Port.zip
I haven't had a chance to take a good look at Jimmy's port, but I think it is the most well documented if nothing else.