code: def test_to_cpu(self, backend_config):
      link = self.create_link()
      link.to_device(backend_config.device)
      self.assertEqual(link.sampler.device, backend_config.device)
      with testing.assert_warns(DeprecationWarning):
          link.to_cpu()
      self.assertEqual(link.sampler.device, backend.CpuDevice())
  
file_path: chainer/tests/chainer_tests/links_tests/loss_tests/test_negative_sampling.py
imports: import unittest
  import numpy
  import chainer
  from chainer import backend
  from chainer.backend import CpuDevice
  from chainer import links
  from chainer import testing
label_desc: Use image node_id 6 for calling the TestNegativeSampling obj's underlying member method code with example usage: obj.test_to_cpu(backend_config) without return types