Hi guys When you remove an Trait from the use: clause you get an DNU because the item in anEvent item is nil. It would be good to fix that. Stef methodChanged: anEvent | cls sel | "cls contains the class in which the method sel has been modified" cls := anEvent item methodClass. (cls inheritsFrom: TestCase) ifFalse: [^ self]. "sel contains the method name that has been modified" sel := anEvent item selector. "this selector has to be a test" (sel beginsWith: 'test') ifFalse: [^ self]. " remove sel from the known test results" TestResult removeFromTestHistory: sel in: cls.