I just wanted some different examples of types of plugin usage, the documentation is a little sparse on cookbook examples. My example:

package MyHungryHippo;
use strict;
use warnings;
use 5.16.0;
use base qw[Template::Plugin];

sub new { 
  my ($class, $context) = @_;
  return bless { _context => $context }, $class;
}

sub nomnom {
  my $self = shift;
  return 'eat it';
}

1;
package main;
use strict;
use warnings;
use 5.16.0;
use Test::More;

use_ok 'MyHungryHippo';
use_ok 'Template';

ok my $tt = Template->new({ PLUGINS => { 'HIPPO' => 'MyHungryHippo' } 
+});

die $tt->error
  if $tt->error;

ok my $tmpl = join('', <DATA>);

ok my $output = $tt->context->process( \$tmpl, {} );

like $output, qr/eat/
  or diag $output;

done_testing();

__DATA__
[% USE HIPPO %]
[%- HIPPO.nomnom() -%]
[download]