code: def test_underscore_in_attribute(self):
      docstring = """
  Attributes
  ----------
  
  arg_ : type
      some description
  """
  
      expected = """
  :ivar arg_: some description
  :vartype arg_: type
  """
  
      config = Config(napoleon_use_ivar=True)
      app = mock.Mock()
      actual = str(NumpyDocstring(docstring, config, app, "class"))
  
      assert expected == actual
  
imports: import re
  from collections import namedtuple
  from inspect import cleandoc
  from textwrap import dedent
  from unittest import mock
  import pytest
  from sphinx.ext.napoleon import Config
  from sphinx.ext.napoleon.docstring import GoogleDocstring, NumpyDocstring, _convert_numpy_type_spec, _recombine_set_tokens, _token_type, _tokenize_type_spec
  from tests.test_extensions.ext_napoleon_pep526_data_google import PEP526GoogleClass
  from tests.test_extensions.ext_napoleon_pep526_data_numpy import PEP526NumpyClass
label_desc: Use image node_id 9 for calling the TestNumpyDocstring obj's underlying member method code with example usage: obj.test_underscore_in_attribute() without return types