Xdebug is code profiling tool for PHP. As such, it is a good addition to PHPUnit. I do a lot of work with CakePHP and CakePHP's built-in test suite makes use of both of these. Install requirements for Xdebug vary from system to system and have changed over the years. Since I'm using Ubuntu 14.04 I thought I would just make a little note of the easiest way to install this on my system.
sudo apt-get install php5-xdebug
sudo service apache2 restart
This will result in the following config file/etc/php5/apache2/conf.d/20-xdebug.ini from there you will be able to apply Xdebug settings.