code: def test_loss_gradient(self, art_warning):
      try:
          transcripts = list()
          audios = list()
          for filename, sample in self.samples.items():
              file_path = get_file(filename, sample["uri"])
              _, audio = read(file_path)
              audios.append(audio)
              transcripts.append(sample["transcript"])
  
          audio_batch = np.array(audios, dtype=object)
          target_batch = np.array(transcripts)
  
          lingvo = TensorFlowLingvoASR()
          gradient_batch = lingvo._loss_gradient_per_batch(
              audio_batch, target_batch
          )
          gradient_sequence = lingvo._loss_gradient_per_sequence(
              audio_batch, target_batch
          )
  
          gradient_batch_sum = np.array(
              [np.abs(gb).sum() for gb in gradient_batch], dtype=object
          )
          gradient_sequence_sum = np.array(
              [np.abs(gs).sum() for gs in gradient_sequence],
              dtype=object,
          )
  
          # test loss gradients per batch and per sequence are the same
          assert_allclose(
              gradient_sequence_sum, gradient_batch_sum, rtol=1e-05
          )
          # test gradient_batch, gradient_sequence and audios items have same shapes
          assert (
              [gb.shape for gb in gradient_batch]
              == [gs.shape for gs in gradient_sequence]
              == [a.shape for a in audios]
          )
      except ARTTestException as e:
          art_warning(e)
  
imports: from __future__ import absolute_import, division, print_function, unicode_literals
  import logging
  import numpy
  import pytest
  from numpy.testing import assert_allclose, assert_array_equal
  from scipy.io.wavfile import read
  from art.estimators.speech_recognition.speech_recognizer import SpeechRecognizerMixin
  from art.estimators.speech_recognition.tensorflow_lingvo import TensorFlowLingvoASR
  from art.estimators.tensorflow import TensorFlowV2Estimator
  from art.utils import get_file
  from tests.utils import ARTTestException
label_desc: Use image node_id 2 for calling the TestTensorFlowLingvoASRLibriSpeechSamples obj's underlying member method code with example usage: obj.test_loss_gradient(art_warning) without return types