code: def test_meltohz_negative(self):
      with assert_warns(UserWarning):
          assert_equal(meltohz(-1, htk=True), 0)
      assert_almost_equal(meltohz(2000, htk=True), 3428.7, decimal=1)
      assert_almost_equal(meltohz(1000, htk=True), 1000.0, 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 3 for calling the aubio_hztomel_htk_test_case obj's underlying member method code with example usage: obj.test_meltohz_negative() without return types