code: def test_mean_diff(self):
      np.testing.assert_almost_equal(mean_diff(const0), 0.0)
      np.testing.assert_almost_equal(mean_diff(const1), 0.0)
      np.testing.assert_almost_equal(mean_diff(constNeg), 0.0)
      np.testing.assert_almost_equal(mean_diff(constF), 0.0)
      np.testing.assert_almost_equal(mean_diff(lin), 1.0)
      np.testing.assert_almost_equal(
          mean_diff(lin0), 1.0526315789473684, decimal=5
      )
      np.testing.assert_almost_equal(
          mean_diff(wave), -3.1442201279407477e-05, decimal=5
      )
      np.testing.assert_almost_equal(
          mean_diff(offsetWave), -3.1442201279407036e-05, decimal=5
      )
      np.testing.assert_almost_equal(
          mean_diff(noiseWave), -0.00010042477181949707, decimal=5
      )
  
imports: import unittest
  import numpy
  from tsfel.feature_extraction.features import *
label_desc: Use image node_id 22 for calling the TestFeatures obj's underlying member method code with example usage: obj.test_mean_diff() without return types