def METHOD_NAME(self):
    class A:
        __metaclass__ = abc.ABCMeta
    class B(object):
        pass
    b = B()
    self.assertFalse(isinstance(b, A))
    self.assertFalse(isinstance(b, (A,)))
    A.register(B)
    self.assertTrue(isinstance(b, A))
    self.assertTrue(isinstance(b, (A,)))