Besides which, the mixin pattern won't *stop* working if we provide this extra functionality - it would just be an alternative for those (like myself) who think it impedes code readability. :-)

At this point we're off topic for the *specific issue*, and I'm fine with our own standard library tests moving to use mixins to support standard unittest invocation. I would suggest the base test cases include Mixin in their name to make it clear how they should be used.