code: def testMelSpectrumAgreesWithGoldenValues(self):
      # Parallel dsp/mfcc:mel_spectrum_test.
      sample_count = 513
      input_ = np.sqrt(np.arange(1, sample_count + 1))[np.newaxis, :]
      spec_to_mel_matrix = mfcc_mel.SpectrogramToMelMatrix(
          num_spectrogram_bins=sample_count,
          audio_sample_rate=22050,
          num_mel_bins=20,
          lower_edge_hertz=20.0,
          upper_edge_hertz=4000.0,
      )
      mel_spectrum = np.dot(input_, spec_to_mel_matrix)
      expected = np.array(
          [
              7.422619,
              10.30330648,
              13.72703292,
              17.24158686,
              21.35253118,
              25.77781089,
              31.30624108,
              37.05877236,
              43.9436536,
              51.80306637,
              60.79867148,
              71.14363376,
              82.90910141,
              96.50069158,
              112.08428368,
              129.96721968,
              150.4277597,
              173.74997634,
              200.86037462,
              231.59802942,
          ]
      )
      np.testing.assert_array_almost_equal(expected, mel_spectrum[0, :])
  
imports: from absl.testing import absltest
  from magenta.models.onsets_frames_transcription import mfcc_mel
  import numpy
label_desc: Use image node_id 1 for calling the MfccMelTest obj's underlying member method code with example usage: obj.testMelSpectrumAgreesWithGoldenValues() without return types