code: def test_backward_cpu(self):
      self.check_backward(self.x, self.output_shape, self.gy)
  
imports: import unittest
  import numpy
  from chainer.backends import cuda
  from chainer import functions
  from chainer import gradient_check
  from chainer import testing
  from chainer.testing import attr
label_desc: Use image node_id 3 for calling the TestResizeImagesBackward obj's underlying member method code with example usage: obj.test_backward_cpu() without return types