code: def testIOProcessor(self):
      size = MPI.COMM_WORLD.Get_size()
      vals = list(range(size))
      vals += [MPI.UNDEFINED, MPI.ANY_SOURCE, MPI.PROC_NULL]
      ioproc = MPI.COMM_WORLD.Get_attr(MPI.IO)
      if ioproc is not None:
          self.assertIn(ioproc, vals)
  
imports: from mpi4py import MPI
  import mpiunittest
  import os
label_desc: Use image node_id 3 for calling the TestWorldAttrs obj's underlying member method code with example usage: obj.testIOProcessor() without return types