code: def test_delete_pred_lock(self):
      cache = caching.PredsCache("test")
      cache_key = [("a", "1"), ("a", "2")]
  
      self.assertIsNone(cache.delete_pred_lock(cache_key))
  
      lock = cache.get_pred_lock(cache_key)
      self.assertEqual(lock, cache.delete_pred_lock(cache_key))
  
      self.assertIsNone(cache.delete_pred_lock(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 4 for calling the PredsCacheTest obj's underlying member method code with example usage: obj.test_delete_pred_lock() without return types