code: def test_activation_backward(self):
      cudnn.activation_backward(self.x, self.y, self.g, self.mode)
  
imports: import sys
  import numpy
  import pytest
  import cupy
  import cupy.cuda.cudnn
  from cupy import testing
label_desc: Use image node_id 3 for calling the TestCudnnActivation obj's underlying member method code with example usage: obj.test_activation_backward() without return types