code: def testRank(self):
      size = self.GROUP.Get_size()
      rank = self.GROUP.Get_rank()
      self.assertTrue(rank >= 0 and rank < size)
  
imports: from mpi4py import MPI
  import mpiunittest
label_desc: Use image node_id 4 for calling the TestGroupWorld obj's underlying member method code with example usage: obj.testRank() without return types