code: def test_batch_backward_gpu(self):
      x_data = cuda.to_gpu(self.x)
      y_grad = cuda.to_gpu(self.gy)
      gradient_check.check_backward(
          self.det, x_data, y_grad, **self.check_backward_options
      )
  
imports: import unittest
  import numpy
  import six
  import chainer
  from chainer.backends import cuda
  from chainer import functions
  from chainer import gradient_check
  from chainer import testing
  from chainer.testing import attr
  from chainer.utils import type_check
label_desc: Use image node_id 14 for calling the DetFunctionTest obj's underlying member method code with example usage: obj.test_batch_backward_gpu() without return types