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 chainer
  from chainer.backends import cuda
  from chainer import gradient_check
  from chainer import testing
  from chainer.testing import attr
  from chainer.testing import condition
  import numpy
  import unittest
  from chainercv import functions
label_desc: Use image node_id 7 for calling the TestPSROIAveragePooling2D obj's underlying member method code with example usage: obj.test_backward_gpu() without return types