When running all the tests, ReleaseTest>>testObsoleteClasses discovers some hundreds of generated classes that are not properly cleaned up. You can also get an inspector on these classes by running: SmalltalkImage current fixObsoleteReferences. (If the result is not empty, an inspector will pop up.) Here are the tests cases responsible for many of these classes: Tests-Traits -- 130 obsolete classes RequiresOriginalTestCase>>testSins creates CAB ... TraitsResource>>setUp creates C1 ... SUnit-Extensions, SUnit-Tests ? ClassFactoryForTestCase>>newName creates ClassForTestToBeDeleted IVsAndClassVarNamesConflictTest>>setUp creates ClassForTestToBeDeleted These sometimes are left as obsolete classes ... Tests-Monticello -- 2 obsolete classes MCFileInTest>> ... creates MCMockClassA MCMockClassG To check this, grab a clean pharo core image, run: SmalltalkImage current fixObsoleteReferences The result should be empty. Then run Tests-Traits (or any of the others) and re-run the expression. You will then see the obsolete classes. Exploring pointers to these classes however does not tell me why they are still hanging around. That's as far as I got. - on