With the increasing complexity of a huge codebase such as provided by Horde there is a significant need for quality control. As p@rdus accumulated a decent amount of experience with a variety of PHP QA tools during the past years it was only natural to apply this knowledge to the Horde codebase.
Many modules - including the Kolab_* packages - are now under constant surveillance of a continous integration server. The system is available for your inspection at ci.horde.org.
The service itself is run by Hudson - the standard CI server these days. The tools deployed on the server are a collection of the latest and greatest in the arena of quality control for PHP. PHPUnit certainly being the most important one as it delivers the framework for unit testing and code coverage analysis. In addition Hudson runs PEAR CodeSniffer (style check), PHP Depend (structural analysis), PHP Mess Detector, and the PHP Copy Paste Detector. On top of this the brand new PHP Code Browser integrates the analysis results into a view of the code.
With this system in place Horde is probably the only PHP based groupware client that can claim to validate its code base against current commercial grade software standards for PHP with each and every commit.