Becoming a KDE Tester
In the early 2000's there was a specific team at KDE which was focused on finding loose ends in KDE applications and tying them together. This was a task of user case studies, writing articles, documentation, creating missing artwork for consistency, and other miscellanea. Ultimately, this team contributed patches of code and documentation that really rounded out the KDE experience.
Communicating with the team
Early 2012 this team was revived and now has a [mailing list] as well as a channel called #kde-quality on irc.freenode.net.