'get_many returns nothing for the dummy cache backend'

def test_get_many(self):

    self.cache.set('a', 'a')
    self.cache.set('b', 'b')
    self.cache.set('c', 'c')
    self.cache.set('d', 'd')
    self.assertEqual(self.cache.get_many(['a', 'c', 'd']), {})
    self.assertEqual(self.cache.get_many(['a', 'b', 'e']), {})
