code: def test_skewness(self):
      self.assertTrue(np.isnan(skewness(const0)))
      self.assertTrue(np.isnan(skewness(const1)))
      self.assertTrue(np.isnan(skewness(constNeg)))
      self.assertTrue(np.isnan(skewness(constF)))
      np.testing.assert_almost_equal(skewness(lin), 0)
      np.testing.assert_almost_equal(
          skewness(lin0), -1.0167718723297815e-16, decimal=5
      )
      np.testing.assert_almost_equal(
          skewness(wave), -2.009718347115232e-17, decimal=5
      )
      np.testing.assert_almost_equal(
          skewness(offsetWave), 9.043732562018544e-16, decimal=5
      )
      np.testing.assert_almost_equal(
          skewness(noiseWave), -0.0004854111290521465, decimal=5
      )
  
imports: import unittest
  import numpy
  from tsfel.feature_extraction.features import *
label_desc: Use image node_id 2 for calling the TestFeatures obj's underlying member method code with example usage: obj.test_skewness() without return types