app/views/helpers/beta.php:

<?php

 class BetaHelper extends Helper {
 	function testing() {
 		echo "Success!";
    }
 }
?>

app/app_controller.php:

class AppController extends AppController{
	 var $helpers = array('Html', 'Menu', 'Beta');
 ...
}

app/views/layouts/default.thtml:

<?php $beta->testing();?>