code: def build_generator(self, task, models, cfg):
      try:
          from examples.speech_recognition.w2l_decoder import (
              W2lViterbiDecoder,
          )
      except Exception:
          raise Exception(
              "Cannot run this test without flashlight dependency"
          )
      with open_dict(cfg):
          cfg.nbest = 1
      return W2lViterbiDecoder(cfg, task.target_dictionary)
  
file_path: fairseq/tests/speech/test_wav2vec2.py
imports: import unittest
  import torch
  from tests.speech import TestFairseqSpeech
  from fairseq.data.data_utils import post_process
  from fairseq import utils
  from omegaconf import open_dict
label_desc: Use image node_id 4 for calling the TestWav2Vec2 obj's underlying member method code with example usage: obj.build_generator(task, models, cfg) and returns: W2lViterbiDecoder