code: def test_hztomel_negative(self):
      with assert_warns(UserWarning):
          assert_equal(hztomel(-1), 0)
  
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 4 for calling the aubio_hztomel_test_case obj's underlying member method code with example usage: obj.test_hztomel_negative() without return types