code: def test_call_cudnn_backrward(self):
      with chainer.using_config("use_cudnn", self.use_cudnn):
          y = self.forward()
          y.grad = self.gy
          patch = "cupy.cudnn.convolution_backward_data"
          with mock.patch(patch) as func:
              y.backward()
              self.assertEqual(
                  func.called, chainer.should_use_cudnn(">=auto")
              )
  
imports: import unittest
  import mock
  import numpy
  import chainer
  from chainer.backends import cuda
  from chainer import functions
  from chainer import links
  from chainer import testing
  from chainer.testing import attr
label_desc: Use image node_id 4 for calling the TestMLPConvolution2DCudnnCall obj's underlying member method code with example usage: obj.test_call_cudnn_backrward() without return types