About debug means ---How to debug a function seperately in an easy way?

Hello, pgsql-hackers:
I want to debug one function in postgre backend.
   for example, I want to debug the following function :

array_set(ArrayType *array,      int nSubscripts,      int *indx,      Datum dataValue,      bool isNull,      int
arraytyplen,     int elmlen,      bool elmbyval,      char elmalign) 
   What I want is to set various inputs, and see the corresponding result.
   Meanwhile , I don't know how to design the test case from the regular process, from TCOP, parser, analyzer,... and
finallyto array_set() 
   I just want to take it in an easy way, for example , I write some code somewhere in postgre backend source
code, and make up many different inputs and see the result returned by this function array_set.
   Is there some convenient way to do it?
   Thanks a lot ^_^

yours sincerely
　　　　　billywq@163.com
　　　　　　　2008-12-15