code: def test_backward_gpu(self):
      self.check_backward(
          cuda.to_gpu(self.pooled_y.array), cuda.to_gpu(self.gy)
      )
  
imports: import unittest
  import numpy
  import chainer
  from chainer.backends import cuda
  import chainer.functions
  from chainer import gradient_check
  from chainer import testing
  from chainer.testing import attr
  from chainer.utils import conv
label_desc: Use image node_id 7 for calling the TestUpsampling2D obj's underlying member method code with example usage: obj.test_backward_gpu() without return types