code: def test_spect_variation(self):
      np.testing.assert_almost_equal(
          spectral_variation(const0, Fs), 1.0
      )
      np.testing.assert_almost_equal(
          spectral_variation(const1, Fs), 1.0
      )
      np.testing.assert_almost_equal(
          spectral_variation(constNeg, Fs), 1.0
      )
      np.testing.assert_almost_equal(
          spectral_variation(constF, Fs), 1.0
      )
      np.testing.assert_almost_equal(
          spectral_variation(lin, Fs), 0.04330670010243309
      )
      np.testing.assert_almost_equal(
          spectral_variation(lin0, Fs), 0.3930601189429277, decimal=5
      )
      np.testing.assert_almost_equal(
          spectral_variation(wave, Fs), 0.9999999999999997, decimal=5
      )
      np.testing.assert_almost_equal(
          spectral_variation(offsetWave, Fs),
          0.9999999999999999,
          decimal=5,
      )
      np.testing.assert_almost_equal(
          spectral_variation(noiseWave, Fs),
          0.9775800433849368,
          decimal=5,
      )
  
imports: import unittest
  import numpy
  from tsfel.feature_extraction.features import *
label_desc: Use image node_id 49 for calling the TestFeatures obj's underlying member method code with example usage: obj.test_spect_variation() without return types