How to tell which CV joint has gone bad?

[rfkellner at snet.net (Rick Kellner)]

I know one of the CV joints in my 91 DD Jetta is on its' way out.  It
will do the classic thumping noise under acceleration.  I plan on
replacing the whole axle with a rebuild however; I only want to replace
the one that has failed.  Is there a way to determine which one has
failed?  Accelerating right or left?  
Finally one of the local chain parts stores has the rebuilds for $69
with a core.  Sure beats putting on a new CV, boots, etc for less money.
Rick.