code: def test_backward_gpu(self):
      with testing.assert_warns(DeprecationWarning):
          self.link.to_gpu()
      x = cuda.to_gpu(self.x)
      if self.learn_b:
          b = None
      else:
          b = cuda.to_gpu(self.b)
      gy = cuda.to_gpu(self.gy)
      self.check_backward(x, b, gy)
  
imports: import unittest
  import numpy
  import chainer
  from chainer.backends import cuda
  from chainer import gradient_check
  from chainer import links
  from chainer import testing
  from chainer.testing import attr
  from chainer.testing import condition
label_desc: Use image node_id 8 for calling the TestBias obj's underlying member method code with example usage: obj.test_backward_gpu() without return types