'Ensure that a class with an abstract parent can be referenced.'

def test_reference_class_with_abstract_parent(self):

    class Sibling(Document, ):
        name = StringField()
        meta = {'abstract': True}
    class Sister(Sibling, ):
        pass
    class Brother(Sibling, ):
        sibling = ReferenceField(Sibling)
    Sister.drop_collection()
    Brother.drop_collection()
    sister = Sister(name='Alice')
    sister.save()
    brother = Brother(name='Bob', sibling=sister)
    brother.save()
    self.assertEquals(Brother.objects[0].sibling.name, sister.name)
