#!/usr/bin/perl
package XYZ;
use warnings;
use strict;
use Pod::Usage;

{
 my $PrivateLexicalData;

 sub do_something_useful {
  ...
 }


} # End of private lexial scope

sub test {
   do_something_useful(3) == 2 or die;
   print "Tests complete\n."
   exit(0);
}

if (not defined caller()) {
    scalar @ARGV == 0 and pod2usage();
    grep { m/-test/i } @ARGV and test();
}

1;

=head1 NAME
...
[download]

Found it! There was another 'XYZ' package with a test sub.