https://bugzilla.wikimedia.org/show_bug.cgi?id=72885
--- Comment #1 from Fabian CommodoreFabianus@gmx.de --- Okay a quick test reveals that the metaclass just checks the variables directly set in the class and not in the subclasses.
In theory the subclass would've to check the subclassed classes and so on and read dry from there. This is for example also when I'm using WikidataTestCase instead of DefaultDrySiteTestCase.