code: def test_hztomel_htk(self):
      for f in np.linspace(0, 20000, 1000):
          assert_almost_equal(
              meltohz_htk(hztomel_htk(f)) - f, 0, decimal=1
          )
      for f in np.linspace(0, 20000, 1000):
          assert_almost_equal(
              hztomel_htk(meltohz_htk(f)) - f, 0, decimal=1
          )
  
imports: from unittest import main
  from numpy.testing import TestCase
  from numpy.testing import assert_equal, assert_almost_equal
  from _tools import assert_warns
  from utils import is32bit
  import numpy
  import aubio
  from aubio import hztomel, meltohz
  from aubio import hztomel_htk, meltohz_htk
label_desc: Use image node_id 5 for calling the aubio_hztomel_htk_test_case obj's underlying member method code with example usage: obj.test_hztomel_htk() without return types