code: def test_downmix(self):
      # test wave loader
      signal, sample_rate = load_wave_file(
          stereo_sample_file, num_channels=1
      )
      self.assertTrue(np.allclose(signal[:5], [35, 35, 31, 33, 33]))
  
      self.assertTrue(len(signal) == 182919)
      self.assertTrue(sample_rate == 44100)
      self.assertTrue(signal.shape == (182919,))
  
imports: from __future__ import absolute_import, division, print_function
  import io
  import unittest
  from os.path import join
  from madmom.io.audio import *
  from .None import AUDIO_PATH, DATA_PATH
label_desc: Use image node_id 5 for calling the TestLoadWaveFileFunction obj's underlying member method code with example usage: obj.test_downmix() without return types