'Ensure we can search for a specific generic reference by
providing its DBRef.'

def test_generic_reference_filter_by_objectid(self):

    class Doc(Document, ):
        ref = GenericReferenceField()
    Doc.drop_collection()
    doc1 = Doc.objects.create()
    doc2 = Doc.objects.create(ref=doc1)
    self.assertTrue(isinstance(doc1.pk, ObjectId))
    doc = Doc.objects.get(ref=doc1.pk)
    self.assertEqual(doc, doc2)
