require_once(PHP/CodeCoverage/Filter.php): failed to open stream

I am trying to get familiar with testing (unit, functional) under Symfony 2.3.24/Windows7/PHP 5.4.7.

It seems PHPUnit is installed correctly (via Composer), but when I run a phpunit -c app/ command I get the following error:

Warning: require_once(PHP/CodeCoverage/Filter.php): failed to open stream: No such file or directory in C:\xampp\php\phpunit on line 38

Fatal error: require_once(): Failed opening required 'PHP/CodeCoverage/Filter.php' (include_path='.;C:\xampp\php\PEAR') in C:\xampp\php\phpunit on line 38

I googled for the issue to no avail. I additionnaly found in the official PHPUnit website that The code coverage report feature requires the Xdebug (2.1.3 or later) and tokenizer extensions.

What do you think about all this? your help is much appreciated.