code: def test_expired(self):
      always_expired = CachedObject.expired()
  
      for dt in Timestamp.min, Timestamp.now(), Timestamp.max:
          with self.assertRaises(Expired):
              always_expired.unwrap(dt)
  
file_path: zipline/tests/utils/test_cache.py
imports: from unittest import TestCase
  from pandas import Timestamp, Timedelta
  from zipline.utils.cache import CachedObject, Expired, ExpiringCache
label_desc: Use image node_id 2 for calling the CachedObjectTestCase obj's underlying member method code with example usage: obj.test_expired() without return types