code: def test_mel_to_hertz(self):
      self.assertEqual(mel_to_hertz(0.0), 0.0)
      self.assertAlmostEqual(mel_to_hertz(150.48910241), 100)
  
      inputs = np.array([150.48910241, 283.22989816])
      expected = np.array([100, 200])
      self.assertTrue(np.allclose(mel_to_hertz(inputs), expected))
  
      self.assertEqual(mel_to_hertz(0.0, "slaney"), 0.0)
      self.assertEqual(mel_to_hertz(1.5, "slaney"), 100)
  
      inputs = np.array([0.9, 1.5, 3.0, 15.0, 15.01453781, 25.08188016])
      expected = np.array([60, 100, 200, 1000, 1001, 2000])
      self.assertTrue(
          np.allclose(mel_to_hertz(inputs, "slaney"), expected)
      )
  
      inputs = np.array(
          [92.6824, 150.4899, 283.2313, 999.9907, 1000.6534, 1521.3674]
      )
      expected = np.array([60, 100, 200, 1000, 1001, 2000])
      self.assertTrue(
          np.allclose(mel_to_hertz(inputs, "kaldi"), expected)
      )
  
      with pytest.raises(ValueError):
          mel_to_hertz(100, mel_scale=None)
  
imports: import unittest
  import numpy
  import pytest
  from transformers.audio_utils import amplitude_to_db, hertz_to_mel, mel_filter_bank, mel_to_hertz, power_to_db, spectrogram, window_function
label_desc: Use image node_id 2 for calling the AudioUtilsFunctionTester obj's underlying member method code with example usage: obj.test_mel_to_hertz() without return types