#!/usr/bin/perl -w
# file somescript.pl

use strict;
use warnings;

sub SubThatNeedsToBeTested {
    # do some stuff
    if ($error ) {
      print "error occurred\n";
      exit 2;
    }
    if ($othererror) {
     print "another error occurred\n";
     exit 3;
    }
}

sub NoNeedToTestThis {
   # ...
}

## main program
&SubThatNeedsToBeTested ();
&NoNeedToTestThis ();
exit 0;