code: def test_multi_node_forward_gpu(self):
      self._check_forward(
          cuda.to_gpu(self.mb_locs),
          cuda.to_gpu(self.mb_confs),
          cuda.to_gpu(self.gt_mb_locs),
          cuda.to_gpu(self.gt_mb_labels),
          self.k,
      )
  
imports: from __future__ import division
  import numpy
  import six
  import unittest
  import chainer
  from chainer.backends import cuda
  import chainer.functions
  from chainer import testing
  from chainermn import create_communicator
  from chainercv.links.model.ssd import multibox_loss
  from chainercv.utils.testing import attr
label_desc: Use image node_id 4 for calling the TestMultiNodeMultiboxLoss obj's underlying member method code with example usage: obj.test_multi_node_forward_gpu() without return types