The testprns program checks a specified printer name against the system printer capabilities (printcap) file.   

It's command line is:

   testprns printername [printcapname]

If printcapname isn't specified, Samba attempts to sue one located in the smb.conf file.   If one isn't specified there, Samba will try /etc/printcap.   If that fails, the program will report an error.