code: def test_functions_are_serializable(self):
      for fn in [
          utils.identity,
          utils.inverse,
          utils.pow_minus_1,
          utils.log2_inverse,
          utils.is_greater_equal_1,
          utils.symmetric_log1p,
      ]:
          self.assertIsNotNone(utils.serialize_keras_object(fn))
  
imports: import tensorflow.compat.v2
  from tensorflow_ranking.python.keras import utils
label_desc: Use image node_id 1 for calling the UtilsTest obj's underlying member method code with example usage: obj.test_functions_are_serializable() without return types