code: def test_index_converts_field_correctly(self):
      vocab = Vocabulary()
      b_index = vocab.add_token_to_namespace("B", namespace="*labels")
      i_index = vocab.add_token_to_namespace("I", namespace="*labels")
      o_index = vocab.add_token_to_namespace("O", namespace="*labels")
  
      tags = ["B", "I", "O", "O", "O"]
      sequence_label_field = SequenceLabelField(
          tags, self.text, label_namespace="*labels"
      )
      sequence_label_field.index(vocab)
  
      assert sequence_label_field._indexed_labels == [
          b_index,
          i_index,
          o_index,
          o_index,
          o_index,
      ]
  
imports: from collections import defaultdict
  import logging
  import pytest
  import numpy
  from allennlp.common.checks import ConfigurationError
  from allennlp.common.testing import AllenNlpTestCase
  from allennlp.data import Token, Vocabulary
  from allennlp.data.fields import TextField, SequenceLabelField
  from allennlp.data.token_indexers import SingleIdTokenIndexer
label_desc: Use image node_id 4 for calling the TestSequenceLabelField obj's underlying member method code with example usage: obj.test_index_converts_field_correctly() without return types