code: def test_username_priorities_of_env_values(self, environ):
      environ.get.return_value = None
      try:
          getpass.getuser()
      except OSError:  # in case there's no pwd module
          pass
      except KeyError:
          # current user has no pwd entry
          pass
      self.assertEqual(
          environ.get.call_args_list,
          [
              mock.call(x)
              for x in ("LOGNAME", "USER", "LNAME", "USERNAME")
          ],
      )
  
imports: import getpass
  import os
  import unittest
  from io import BytesIO, StringIO, TextIOWrapper
  from unittest import mock
  from test import support
label_desc: Use image node_id 2 for calling the GetpassGetuserTest obj's underlying member method code with example usage: obj.test_username_priorities_of_env_values(environ) without return types