Is there a way to check if my javascript files are being served gzipped?

I have followed a post that explains how to do it but when I test my site through this tool:
[websiteoptimization.com...]

It tells me I could compress the files. As far as I know, I have!

The method I've used is in my javascript folder I have the following .htaccess file

AddHandler application/x-httpd-php .css
php_value auto_prepend_file gzip-js.php
php_flag zlib.output_compression On

I also have the following file named gzip-js.php

<?php
  ob_start ("ob_gzhandler");
  header("Content-type: text/javascript; charset: UTF-8");
  header("Cache-Control: must-revalidate");
  $offset = 60 * 60 ;
  $ExpStr = "Expires: " .
  gmdate("D, d M Y H:i:s",
  time() + $offset) . " GMT";
  header($ExpStr);
?>

Should this work, and if so how can I test it?

Thanks!