code: def test_forward_gpu(self):
      with chainer.using_config("use_cudnn", self.use_cudnn):
          self.check_forward(
              cuda.to_gpu(self.x), cuda.to_gpu(self.grid)
          )
  
imports: import unittest
  import numpy
  import chainer
  from chainer.backends import cuda
  from chainer import functions
  from chainer import gradient_check
  from chainer import testing
  from chainer.testing import attr
  from chainer.testing import condition
  from chainer import Variable
label_desc: Use image node_id 4 for calling the TestSpatialTransformerSamplerForwardToyCases obj's underlying member method code with example usage: obj.test_forward_gpu() without return types