具有全局短代码的弹出窗口中的自定义内容？

I have a popup that loads on entry and want custom content specified within each post, specified by the shortcode [test rating=3], to be loaded in the popup (in this case 3). Here is my php:

<?php
add_shortcode('test', 'test_function');
function test_function($atts){
    global $post;
    extract(shortcode_atts(array(
     'rating' => '5'
    ), $atts));
    return $rating;
}
?>

In the code for the entry popup if I use [test] it doesn't pull the value of rating specified per [test rating=3] in the post (instead it just returns the default value 5). How should this be done?