code: def test_variance(self):
      np.testing.assert_almost_equal(calc_var(const0), 0.0)
      np.testing.assert_almost_equal(calc_var(const1), 0.0)
      np.testing.assert_almost_equal(calc_var(constNeg), 0.0)
      np.testing.assert_almost_equal(calc_var(constF), 0.0)
      np.testing.assert_almost_equal(calc_var(lin), 33.25)
      np.testing.assert_almost_equal(
          calc_var(lin0), 36.84210526315789, decimal=5
      )
      np.testing.assert_almost_equal(calc_var(wave), 0.5, decimal=5)
      np.testing.assert_almost_equal(
          calc_var(offsetWave), 0.5, decimal=5
      )
      np.testing.assert_almost_equal(
          calc_var(noiseWave), 0.5081167177369529, decimal=5
      )
  
imports: import unittest
  import numpy
  from tsfel.feature_extraction.features import *
label_desc: Use image node_id 8 for calling the TestFeatures obj's underlying member method code with example usage: obj.test_variance() without return types