code: def test_multi_class_from_file(self):
      f = tempfile.NamedTemporaryFile(mode="w", delete=False)
      f.writelines("\n".join(["abc", "bcd", "def", "efg"]))
      f.close()
      config = OmegaConf.create({"vocab_file": f.name})
      processor = MultiClassFromFile(config)
  
      output = processor({"label": "abc"})
      self.assertEqual(output["class_index"], 0)
      output = processor({"label": "efg"})
      self.assertEqual(output["class_index"], 3)
      output = processor("def")
      self.assertEqual(output["class_index"], 2)
  
      self.assertRaises(AssertionError, processor, {"label": "UNK"})
      os.unlink(f.name)
  
imports: import os
  import tempfile
  import unittest
  import torch
  from mmf.datasets.processors.image_processors import VILTImageProcessor
  from mmf.datasets.processors.processors import CaptionProcessor, EvalAIAnswerProcessor, MultiClassFromFile, MultiHotAnswerFromVocabProcessor, Processor, TransformerBboxProcessor
  from mmf.datasets.processors.video_processors import VideoTransforms
  from mmf.utils.configuration import load_yaml
  from omegaconf import OmegaConf
  from tests.test_utils import compare_tensors, skip_if_no_pytorchvideo
label_desc: Use image node_id 6 for calling the TestDatasetProcessors obj's underlying member method code with example usage: obj.test_multi_class_from_file() without return types