code: def test_forward_gpu(self):
      self.check_forward(
          cuda.to_gpu(self.s), cuda.to_gpu(self.i), cuda.to_gpu(self.x)
      )
  
imports: import unittest
  import numpy
  import chainer
  from chainer import backend
  from chainer import cuda
  from chainer import testing
  from chainer.testing import attr
  import thin_stack
label_desc: Use image node_id 4 for calling the TestThinStackSet obj's underlying member method code with example usage: obj.test_forward_gpu() without return types