If it's a Gore Tex fabric McNett makes Gore Tex patches, I think they are about 7 bucks for two 3-4" round patches. I haven't used the patches but will be soon to fix some holes in the sleeve of my Gore Tex jacket.
As far as leak testing I'd imagine you could just rubberband the wrist shut then fill the sleeve with water and wait to see if you spring some little leaks?
edit: McNett Hunting and fishing says you can look for pinholes in a drysuit this way -To find pinhole leaks in Gore-Tex® fabric dry suits: 1) Turn the suit inside out. 2) Soak the tip of a rag in rubbing alcohol and dab over the suspect area. 3) The hole will show up as a contrasting color. Allow area to dry and seal (on the inside surface) with Aquaseal®.
Link here: http://www.mcnett-hunting.com/Repair...-Care/434.aspx