code: def test_minimal_pert_preproc(self) -> None:
      model = BasicModel_MultiLayer()
      text_inp = ["abc", "zyd", "ghi"]
      minimal_pert = MinParamPerturbation(
          forward_func=model,
          attack=add_char,
          arg_name="char_val",
          arg_min=0,
          arg_max=26,
          arg_step=1,
          preproc_fn=text_preproc_fn,
          apply_before_preproc=True,
      )
      target_inp, pert = minimal_pert.evaluate(
          text_inp, target=1, attack_kwargs={"ind": 1}
      )
      self.assertEqual(pert, None)
      self.assertEqual(target_inp, None)
  
file_path: captum/tests/robust/test_min_param_perturbation.py
imports: from typing import cast, List
  import torch
  from captum.robust import MinParamPerturbation
  from tests.helpers.basic import assertTensorAlmostEqual, BaseTest
  from tests.helpers.basic_models import BasicModel, BasicModel_MultiLayer
  from torch import Tensor
label_desc: Use image node_id 3 for calling the Test obj's underlying member method code with example usage: obj.test_minimal_pert_preproc() without return types