Problem with abstract classes

The following test:

    def test_remove_with_abstract_class_inheritance(self):
        @six.add_metaclass(abc.ABCMeta)
        class AbstractSerializer(object):
            pass

        @removals.remove(version="2.9", removal_version="3.0")
        class ConcreteSerializer(AbstractSerializer):
            pass

        class MyConcreteSerializer(ConcreteSerializer):
            pass

        MyConcreteSerializer()

Ends up with the following error in python 2.7:

Traceback (most recent call last):
  File "debtcollector/tests/test_deprecation.py", line 546, in test_remove_with_abstract_class_inheritance
    class MyConcreteSerializer(ConcreteSerializer):
  File "/Users/dims/openstack/oslo/debtcollector/.tox/py27/bin/../lib/python2.7/abc.py", line 87, in __new__
    cls = super(ABCMeta, mcls).__new__(mcls, name, bases, namespace)
TypeError: Error when calling the metaclass bases
    metaclass conflict: the metaclass of a derived class must be a (non-strict) subclass of the metaclasses of all its bases

And ends up with the following error in python 3.4:

Traceback (most recent call last):
  File "/Users/dims/openstack/oslo/debtcollector/debtcollector/tests/test_deprecation.py", line 549, in test_remove_with_abstract_class_inheritance
    MyConcreteSerializer()
TypeError: 'tuple' object is not callable