class_docstr: Tests for bluefog/torch/mpi_ops.py on one-sided communication.
code: def cast_and_place(tensor, dtype):
      if dtype.is_cuda:
          if (
              bf.nccl_built()
              and bf.local_size() > torch.cuda.device_count()
          ):
              raise EnvironmentError(
                  "Cannot run number of processes in one machine more than GPU device count"
                  " in NCCL environment"
              )
          return tensor.cuda(
              bf.local_rank() % torch.cuda.device_count()
          ).type(dtype)
      return tensor.type(dtype)
  
imports: from __future__ import absolute_import
  from __future__ import division
  from __future__ import print_function
  import inspect
  import itertools
  import time
  import warnings
  import unittest
  from bluefog.common import topology_util
  import bluefog.torch
  import torch
  import numpy
label_desc: Use image node_id 4 for calling the WinOpsTests obj's underlying member method code with example usage: obj.cast_and_place(tensor, dtype) and returns: tensor, tensor