code: def test_pred_lock_key_no_concurrent_predictions(self):
      cache = caching.PredsCache("test", False)
      cache_key = [("a", "1"), ("a", "2")]
  
      self.assertIsNone(cache.pred_lock_key(cache_key))
  
      cache.get_pred_lock(cache_key)
      expected_cache_key = frozenset(
          [caching.PRED_LOCK_KEY_WHEN_NO_CONCURRENT_ACCESS]
      )
      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.assertEqual(
          expected_cache_key, 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 3 for calling the PredsCacheTest obj's underlying member method code with example usage: obj.test_pred_lock_key_no_concurrent_predictions() without return types