code: def test_add_go_token(self):
      model = self._get_neural_hmm()
      (
          input_dummy,
          input_lengths,
          mel_spec,
          mel_lengths,
      ) = self._get_embedded_input()
  
      out = model._add_go_token(
          mel_spec
      )  # pylint: disable=protected-access
      self.assertEqual(out.shape, mel_spec.shape)
      self.assertTrue(
          (out[:, 1:] == mel_spec[:, :-1]).all(),
          "Go token not appended properly",
      )
  
imports: import os
  import random
  import unittest
  from copy import deepcopy
  import torch
  from tests import get_tests_output_path
  from TTS.tts.configs.overflow_config import OverflowConfig
  from TTS.tts.layers.overflow.common_layers import Encoder, Outputnet, OverflowUtils
  from TTS.tts.layers.overflow.decoder import Decoder
  from TTS.tts.layers.overflow.neural_hmm import EmissionModel, NeuralHMM, TransitionModel
  from TTS.tts.models.overflow import Overflow
  from TTS.tts.utils.helpers import sequence_mask
  from TTS.utils.audio import AudioProcessor
label_desc: Use image node_id 8 for calling the TestNeuralHMM obj's underlying member method code with example usage: obj.test_add_go_token() without return types