code: def testAlltoall(self):
      size = self.COMM.Get_size()
      rank = self.COMM.Get_rank()
      for array, typecode in arrayimpl.loop():
          for root in range(size):
              check = arrayimpl.scalar(root)
              sbuf = array(root, typecode, (size, root + 1))
              rbuf = array(-1, typecode, (size, root + 1))
              self.COMM.Alltoall(sbuf.as_mpi(), rbuf.as_mpi_c(root + 1))
              for value in rbuf.flat:
                  self.assertEqual(value, check)
  
imports: from mpi4py import MPI
  import mpiunittest
  import arrayimpl
  from functools import reduce
label_desc: Use image node_id 6 for calling the BaseTestCCOBuf obj's underlying member method code with example usage: obj.testAlltoall() without return types