code: def test_backward_gpu(self):
      with testing.assert_warns(DeprecationWarning):
          self.rnn.to_gpu()
      with chainer.using_config("use_cudnn", "auto"):
          self.check_backward(
              cuda.to_gpu(self.h),
              cuda.to_gpu(self.c),
              [cuda.to_gpu(x) for x in self.xs],
              cuda.to_gpu(self.gh),
              cuda.to_gpu(self.gc),
              [cuda.to_gpu(gy) for gy in self.gys],
          )
  
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
label_desc: Use image node_id 12 for calling the TestNStepBiLSTM obj's underlying member method code with example usage: obj.test_backward_gpu() without return types