Hi Damien, this is SUnit, it is exactly the same in Squeak. There are two major problems with this approach: * It introduces a direct class reference, renaming the class TestResource breaks the implementation. * It only works for flat hierarchies where you have an abstract superclass and all the direct or indirect subclasses are concrete, unless you re-implement #isAbstract. In Pier and Magritte there are mostly many abstract classes inheriting from each other. The advantage of this approach is: * You only need to implement #isAbstract if you introduce a new abstract class, otherwise the answer is already correct. Maybe other people have other advantages/disadvantages? Or other ideas how to solve this particular problem. Not to mention that #isAbstract could be also calculated dynamically ... Cheers, Lukas -- Lukas Renggli http://www.lukas-renggli.ch