Class BA

Lib/test/test_sys.py:1862–1863

        # non-empty __slots__
        check = self.check_slots
        class BA(bytearray):
            __slots__ = 'a', 'b', 'c'
        check(BA(), bytearray(), '3P')
        class D(dict):
            __slots__ = 'a', 'b', 'c'