DataEngineTracker is a simple class that follows all activity in a given Plasma::DataEngine.
Simply add it to your project and then instantiate it with a Plasma::DataEngine* as the first parameter. This will let you watch sources as they are added, removed and change state. Very handy to see how a Plasma::DataEngine is being used and behaving, and as such useful for both DataEngine authors as well as those writing code using DataEngines.