code: def test_global_config_singleton(self):
      global_config_1 = NiftyNetGlobalConfig()
      global_config_2 = NiftyNetGlobalConfig()
      self.assertEqual(global_config_1, global_config_2)
      self.assertTrue(global_config_1 is global_config_2)
  
imports: from glob import glob
  from os import remove, makedirs
  from os.path import expanduser, join, isdir, isfile
  from os.path import getmtime
  from shutil import rmtree
  from unittest import TestCase
  from niftynet.utilities.niftynet_global_config import NiftyNetGlobalConfig
label_desc: Use image node_id 2 for calling the TestGlobalConfigSingleton obj's underlying member method code with example usage: obj.test_global_config_singleton() without return types