/**
     * Start up
     */
    public function __construct()
    {
        add_action( 'admin_menu', array( $this, 'add_amazon_affiliate_products_page' ) );
        add_action( 'admin_init', array( $this, 'page_init' ) );
        add_shortcode( 'test123shortcode', 'testShortcode');
    }

 /**
 * SHORTCODE output
 */
function testShortcode()
{
  $output .='<h1>testing shortcode its working if you see this...</h1>';
  return $output;
}