code: def mock_model_fn(adv_input, is_train, reuse):
      """Mock model_fn that returns input directly."""
      del is_train, reuse
      return adv_input
  
file_path: neural-structured-learning/neural_structured_learning/lib/regularizer_test.py
imports: from __future__ import absolute_import
  from __future__ import division
  from __future__ import print_function
  import neural_structured_learning.configs
  from neural_structured_learning.lib import regularizer
  import numpy
  import tensorflow
label_desc: Use image node_id 1 for calling a global function with example usage: mock_model_fn(adv_input, is_train, reuse) and returns: adv_input