code: def testGatherv(self):
      comm = self.INTERCOMM
      rank = comm.Get_rank()
      size = comm.Get_size()
      rsize = comm.Get_remote_size()
      for array, typecode in arrayimpl.loop():
          for color in (0, 1):
              if self.COLOR == color:
                  for root in range(size):
                      if root == rank:
                          rbuf = array(
                              -1, typecode, (rsize, root + color)
                          )
                          comm.Gatherv(
                              None, rbuf.as_mpi(), root=MPI.ROOT
                          )
                          check = arrayimpl.scalar(root)
                          for value in rbuf.flat:
                              self.assertEqual(value, check)
                      else:
                          comm.Gatherv(None, None, root=MPI.PROC_NULL)
              else:
                  for root in range(rsize):
                      sbuf = array(root, typecode, root + color)
                      comm.Gatherv(sbuf.as_mpi(), None, root=root)
  
file_path: mpi4py/test/test_cco_vec_inter.py
imports: from mpi4py import MPI
  import mpiunittest
  import arrayimpl
label_desc: Use image node_id 3 for calling the BaseTestCCOVecInter obj's underlying member method code with example usage: obj.testGatherv() without return types