code: def test_pk_pk_distance(self):
      np.testing.assert_almost_equal(pk_pk_distance(const0), 0.0)
      np.testing.assert_almost_equal(pk_pk_distance(const1), 0.0)
      np.testing.assert_almost_equal(pk_pk_distance(constNeg), 0.0)
      np.testing.assert_almost_equal(pk_pk_distance(constF), 0.0)
      np.testing.assert_almost_equal(pk_pk_distance(lin), 19)
      np.testing.assert_almost_equal(pk_pk_distance(lin0), 20.0)
      np.testing.assert_almost_equal(pk_pk_distance(wave), 2.0)
      np.testing.assert_almost_equal(pk_pk_distance(offsetWave), 2.0)
      np.testing.assert_almost_equal(
          pk_pk_distance(noiseWave), 2.4800109800001993
      )
  
imports: import unittest
  import numpy
  from tsfel.feature_extraction.features import *
label_desc: Use image node_id 31 for calling the TestFeatures obj's underlying member method code with example usage: obj.test_pk_pk_distance() without return types