code: def test_call_gpu(self):
      self.link.to_gpu()
      self._check_call(
          chainer.backends.cuda.to_gpu(self.x),
          self.img_size,
          self.scales,
      )
  
file_path: chainercv/tests/links_tests/model_tests/faster_rcnn_tests/test_region_proposal_network.py
imports: import numpy
  import unittest
  import chainer
  from chainer.backends import cuda
  from chainer import testing
  from chainer.testing import attr
  from chainercv.links.model.faster_rcnn import RegionProposalNetwork
label_desc: Use image node_id 4 for calling the TestRegionProposalNetwork obj's underlying member method code with example usage: obj.test_call_gpu() without return types