code: def test_backward_gpu(self):
      self.check_backward(
          cuda.to_gpu(self.x),
          cuda.to_gpu(self.rois),
          cuda.to_gpu(self.roi_indices),
          cuda.to_gpu(self.gy),
      )
  
imports: import unittest
  import numpy
  import chainer
  from chainer import cuda
  from chainer import functions
  from chainer import gradient_check
  from chainer import testing
  from chainer.testing import attr
  from chainer.testing import condition
  from chainer_tests.functions_tests.pooling_tests import pooling_nd_helper
label_desc: Use image node_id 8 for calling the TestROIMaxAlign2D obj's underlying member method code with example usage: obj.test_backward_gpu() without return types