<?php
/*
Plugin Name: add_filter test
Plugin URI: http://matsu.tymy.net/
Description: Contents rewrite test
Version: 1.0.1
Author: Yuki Matsukura
Author URI: http://matsu.tymy.net/
*/
function myfunction($content) {
        print 'this block is passed.';
        $content = 'test'.$content;
        return $content;
}
add_filter('the_content', 'myfunction');