For scripts, run them as cactiuser from cli to check basic functionality. E.g. for a perl script named your-perl-script.pl with parameters "p1 p2" under *nix this would look like:
su - cactiuser /full/path/to/perl your-perl-script.pl p1 p2 ... (check output)
For snmp, snmpget the _exact_ OID you're asking for, using same community string and snmp version as defined within cacti. For an OID of .1.3.6.1.4.something, community string of very-secret and version 2 for target host target-host this would look like
snmpget -c very-secret -v 2c target-host .1.3.6.1.4.something .... (check output)