code: def testDifference(self):
      group = MPI.Group.Difference(MPI.GROUP_EMPTY, self.GROUP)
      self.assertEqual(
          MPI.Group.Compare(group, MPI.GROUP_EMPTY), MPI.IDENT
      )
      group.Free()
      group = MPI.Group.Difference(self.GROUP, MPI.GROUP_EMPTY)
      self.assertEqual(MPI.Group.Compare(group, self.GROUP), MPI.IDENT)
      group.Free()
      group = MPI.Group.Difference(self.GROUP, self.GROUP)
      self.assertEqual(
          MPI.Group.Compare(group, MPI.GROUP_EMPTY), MPI.IDENT
      )
      group.Free()
  
imports: from mpi4py import MPI
  import mpiunittest
label_desc: Use image node_id 5 for calling the BaseTestGroup obj's underlying member method code with example usage: obj.testDifference() without return types