code: def test_backward_zero_input_gpu(self):
      self.check_backward_zero_input(cuda.to_gpu(self.zero_x))
  
imports: import unittest
  import numpy
  import chainer
  from chainer.backends import cuda
  from chainer import distributions
  from chainer import gradient_check
  from chainer import testing
  from chainer.testing import attr
label_desc: Use image node_id 13 for calling the TestModifiedXLogX obj's underlying member method code with example usage: obj.test_backward_zero_input_gpu() without return types