My first plugin. Why doesn't it work? And how to debug?

This is my first Plugin. I coded it by viewing some tutorials… but it doesnt work 🙁

I try to set the shortcode [randteasers] to my WP Blog and nothing happens… its not parsed…

<?php

/*
   Plugin Name: Random Pageteasers
   Plugin URI: http://www.iscope.de
   Description: Show teasers for random pages
   Author: Fabian Heinrich <fheinrich@iscope.de>
   Author URI: http://www.iscope.de
   Version: 0.0.1
*/

if(!class_exists('randTeasers')) {

	class randTeasers {

		function __construct() {
			var_dump('CONSTRUCTOR');
			register_activation_hook( __FILE__, array(&$this, 'activate'));
			register_deactivation_hook( __FILE__, array(&$this, 'deactivate'));
		}

		function activate() {
			// Code to execute when the plugin is activated (for example set actions & filters)
			// ...
			var_dump('ACTIVATED');
		}

		function deactivate() {
			// Code to execute when the plugin is deactivated (for example remove actions & filters)
			remove_shortcode('pageteasers');
			var_dump('DEACTIVATED');
		}

		// New filtering function that will add a where clause to the query
		function filter_where($where = '') {
			// Pages from the last x days
			$where .= " AND post_date > '" . date('Y-m-d', strtotime('-8 days')) . "'";
			return $where;
		}

		function getRandomTeasers() {
			// Add filter for sql-where clause
			add_filter('posts_where', array(&$this, 'filter_where'));

			// Add arguments for WP_Query
			$args = array(
				'orderby' => 'rand',
				'post_type' => 'page',
				'post_status' => 'publish',
				'posts_per_page' => 4,
				'caller_get_posts'=> 1
			);

			// Initialize WP_Query with arguments
			$my_query = null;
			$my_query = new WP_Query($args);

			// Execute query, receive page data and build html
			if ($my_query->have_posts()) {

				while ($my_query->have_posts()) {

					$my_query->the_post();
					echo "<p><a href=\"".the_permalink()."\" rel=\"bookmark\" title=\"Permanent Link to ".the_title_attribute()."\">".the_title()."</a> (vom ".get_the_date().")</p>";

				}

			}

			// Remove filter for sql-where clause
			remove_filter('posts_where', array(&$this, 'filter_where'));

			// Restore global post data stomped by the_post().
			wp_reset_query();
		}

	}

} else {

	$randTeasersObject = new randTeasers();
	var_dump('TEST2');

	if (isset($randTeasersObject)) {
		var_dump('TEST1');
		// Add wordpress init-action for plugin-activation
		add_action('init', array(&$randTeasersObject, 'activate'));

		// Add wordpress shortcode
		add_shortcode('randtreasers', array(&$randTeasersObject, 'getRandomTeasers'));
	}

}

?>