'Test we can follow a m2m and another m2m'

def test_m2m_then_m2m(self):

    with self.assertNumQueries(3):
        qs = Author.objects.prefetch_related(u'books__read_by')
        lists = [[[six.text_type(r) for r in b.read_by.all()] for b in a.books.all()] for a in qs]
        self.assertEqual(lists, [[[u'Amy'], [u'Belinda']], [[u'Amy']], [[u'Amy'], []], [[u'Amy', u'Belinda']]])
