Two ways to test it:
1. Stick it in 6th when pootling along (30-40MPH) and floor it. If the revs rise quicker than the speed then its on its way out (it will be obvious)
2. Put the handbrake on and put it in gear. Let the clutch out. If it stalls you're ok, if it doesnt, erm, time for a new clutch, now! Not sure i Like the sounds of this method though, prefer the one above.