code: def test_with_token_characters_indexer(self):
      inputs = {"sentence": "I always write unit tests for my code."}
  
      archive = load_archive(
          self.FIXTURES_ROOT
          / "basic_classifier"
          / "serialization"
          / "model.tar.gz"
      )
      predictor = Predictor.from_archive(archive)
      predictor._dataset_reader._token_indexers[
          "chars"
      ] = TokenCharactersIndexer(min_padding_length=1)
      predictor._model._text_field_embedder._token_embedders[
          "chars"
      ] = EmptyEmbedder()
  
      hotflipper = Hotflip(predictor)
      hotflipper.initialize()
      attack = hotflipper.attack_from_json(
          inputs, "tokens", "grad_input_1"
      )
      assert attack is not None
      assert "final" in attack
      assert "original" in attack
      assert "outputs" in attack
      assert len(attack["final"][0]) == len(
          attack["original"]
      )  # hotflip replaces words without removing
  
      # This checks for a bug that arose with a change in the pytorch API.  We want to be sure we
      # can handle the case where we have to re-encode a vocab item because we didn't save it in
      # our fake embedding matrix (see Hotflip docstring for more info).
      hotflipper = Hotflip(predictor, max_tokens=50)
      hotflipper.initialize()
      hotflipper._first_order_taylor(
          grad=torch.rand((10,)).numpy(),
          token_idx=torch.tensor(60),
          sign=1,
      )
  
file_path: allennlp/tests/interpret/hotflip_test.py
imports: from pytest import raises
  import torch
  from allennlp.common.testing import AllenNlpTestCase
  from allennlp.data.token_indexers import TokenCharactersIndexer
  from allennlp.interpret.attackers import Hotflip
  from allennlp.models.archival import load_archive
  from allennlp.modules.token_embedders import EmptyEmbedder
  from allennlp.predictors import Predictor, TextClassifierPredictor
  from allennlp.data.dataset_readers import TextClassificationJsonReader
  from allennlp.data.vocabulary import Vocabulary
  from allennlp.common.testing.interpret_test import FakeModelForTestingInterpret, FakePredictorForTestingInterpret
label_desc: Use image node_id 2 for calling the TestHotflip obj's underlying member method code with example usage: obj.test_with_token_characters_indexer() without return types