code: def test_pred_lock_key(self):
      cache = caching.PredsCache("test")
      cache_key = [("a", "1"), ("a", "2")]
  
      self.assertIsNone(cache.pred_lock_key(cache_key))
  
      cache.get_pred_lock(cache_key)
      expected_cache_key = frozenset(cache_key)
      self.assertEqual(
          expected_cache_key, cache.pred_lock_key(cache_key)
      )
  
      sub_cache_key = [("a", "1")]
      self.assertEqual(
          expected_cache_key, cache.pred_lock_key(sub_cache_key)
      )
  
      mismatch_cache_key = [("b", "1")]
      self.assertIsNone(cache.pred_lock_key(mismatch_cache_key))
  
imports: from absl.testing import absltest
  from absl.testing import parameterized
  from lit_nlp.api import dataset
  from lit_nlp.lib import caching
  from lit_nlp.lib import testing_utils
label_desc: Use image node_id 2 for calling the PredsCacheTest obj's underlying member method code with example usage: obj.test_pred_lock_key() without return types