code: def _export(self, model, filepath, serving_default="regress"):
      signatures = saved_model_lib.Signatures(
          model=model,
          context_feature_spec=CONTEXT_FEATURE_SPEC,
          example_feature_spec=EXAMPLE_FEATURE_SPEC,
          mask_feature_name=_MASK,
      )(serving_default)
      model.save(
          filepath=filepath, signatures=signatures, save_format="tf"
      )
  
file_path: ranking/tensorflow_ranking/python/keras/saved_model_test.py
imports: import tensorflow
  from google.protobuf import text_format
  from tensorflow_ranking.python.keras import saved_model
  from tensorflow_serving.apis import input_pb2
label_desc: Use image node_id 2 for calling the SignaturesTest obj's underlying member method code with example usage: obj._export(model, filepath, serving_default) without return types