code: def test_hztomel(self):
      assert_equal(hztomel(0, htk=True), 0)
      assert_almost_equal(hztomel(3428.7, htk=True), 2000.0, decimal=1)
      assert_almost_equal(hztomel(6300, htk=True), 2595.0, 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 2 for calling the aubio_hztomel_htk_test_case obj's underlying member method code with example usage: obj.test_hztomel() without return types