code: def test_to_gpu(self):
      self.coder.to_gpu()
      self.assertEqual(self.coder.xp, cuda.cupy)
  
file_path: chainercv/tests/links_tests/model_tests/ssd_tests/test_multibox_coder.py
imports: import numpy
  import unittest
  from chainer.backends import cuda
  from chainer import testing
  from chainer.testing import attr
  from chainercv.links.model.ssd import MultiboxCoder
label_desc: Use image node_id 3 for calling the TestMultiboxCoder obj's underlying member method code with example usage: obj.test_to_gpu() without return types