helpful functions in R for testing results of tree ("party")

Hello all.

   I  have  been  teaching myself how to use recursive partitioning in R,
   particularly using the "party" package.

   Now that i've generated some trees, i would like to understand how i would
   go about validating the goodness of fit/accuracy, etc..., of the trees. What
   functions can i use?  Do i need to validate each terminal node separately?
   Are there examples that i could review which would make this more easily
   understood?

   Thanks in advance for your help.

   Sean