code: def testConstructor(self):
      group = MPI.Group()
      self.assertIsNot(group, MPI.GROUP_NULL)
      self.assertEqual(group, MPI.GROUP_NULL)
  
imports: from mpi4py import MPI
  import mpiunittest
label_desc: Use image node_id 1 for calling the TestGroupNull obj's underlying member method code with example usage: obj.testConstructor() without return types