This is the error that I was getting.
PHP Warning: require_once(PHP/CodeCoverage/Filter.php): failed to open stream: No such file or directory in /usr/bin/phpunit on line 38 PHP Fatal error: require_once(): Failed opening required 'PHP/CodeCoverage/Filter.php' (include_path='.:/usr/share/php:/usr/share/pear') in /usr/bin/phpunit on line 38
There were lots of talk on Google about people who suffered the same problem. It took me a while to work out what was going on
It turns out that somewhere along the way the dependancies of PHPUnit have changed and I needed to update the PEAR packages (including the root PEAR installer) and add a couple new ones too.
This should get you back on track if you are having the same problems.
sudo -s pear channel-discover pear.phpunit.de pear channel-discover pear.symfony-project.com pear channel-discover components.ez.no pear upgrade-all pear install --alldeps phpunit/PHPUnit