code: def testArgsOnlyAtRoot(self):
      self.COMM.Barrier()
      if self.COMM.Get_rank() == self.ROOT:
          child = self.COMM.Spawn(
              self.COMMAND,
              self.ARGS,
              self.MAXPROCS,
              info=self.INFO,
              root=self.ROOT,
          )
      else:
          child = self.COMM.Spawn(
              None,
              None,
              -1,
              info=MPI.INFO_NULL,
              root=self.ROOT,
          )
      child.Barrier()
      child.Disconnect()
      self.COMM.Barrier()
  
imports: from mpi4py import MPI
  import mpiunittest
  import sys, os, mpi4py
label_desc: Use image node_id 3 for calling the BaseTestSpawnSingle obj's underlying member method code with example usage: obj.testArgsOnlyAtRoot() without return types