code: def testBSendAndRecv(self):
      buf = MPI.Alloc_mem((1 << 16) + MPI.BSEND_OVERHEAD)
      MPI.Attach_buffer(buf)
      try:
          size = self.COMM.Get_size()
          rank = self.COMM.Get_rank()
          for smess in messages:
              self.COMM.bsend(smess, MPI.PROC_NULL)
              rmess = self.COMM.recv(None, MPI.PROC_NULL, 0)
              self.assertIsNone(rmess)
          if size == 1:
              return
          for smess in messages:
              if rank == 0:
                  self.COMM.bsend(smess, rank + 1, 0)
                  rmess = smess
              elif rank == size - 1:
                  rmess = self.COMM.recv(None, rank - 1, 0)
              else:
                  rmess = self.COMM.recv(None, rank - 1, 0)
                  self.COMM.bsend(rmess, rank + 1, 0)
              self.assertEqual(rmess, smess)
      finally:
          MPI.Detach_buffer()
          MPI.Free_mem(buf)
  
imports: from mpi4py import MPI
  from mpi4py.util import pkl5
  import sys, os
label_desc: Use image node_id 7 for calling the BaseTest obj's underlying member method code with example usage: obj.testBSendAndRecv() without return types