code: def test_label_field_can_index_with_vocab(self):
      vocab = Vocabulary()
      vocab.add_token_to_namespace("entailment", namespace="labels")
      vocab.add_token_to_namespace("contradiction", namespace="labels")
      vocab.add_token_to_namespace("neutral", namespace="labels")
  
      label = LabelField("entailment")
      label.index(vocab)
      tensor = label.as_tensor(label.get_padding_lengths())
      assert tensor.item() == 0
  
file_path: magnitude/pymagnitude/third_party/allennlp/tests/data/fields/label_field_test.py
imports: from __future__ import with_statement
  from __future__ import absolute_import
  from __future__ import print_function
  import pytest
  from allennlp.common.checks import ConfigurationError
  from allennlp.common.testing import AllenNlpTestCase
  from allennlp.data.fields import LabelField
  from allennlp.data import Vocabulary
label_desc: Use image node_id 2 for calling the TestLabelField obj's underlying member method code with example usage: obj.test_label_field_can_index_with_vocab() without return types