code: def test_forward_gpu(self):
      self.check_forward(cuda.to_gpu(self.x))
  
imports: import unittest
  from chainer import cuda
  from chainer import testing
  from chainer.testing import attr
  from chainer.testing import condition
  import numpy
  from chainerrl.functions.mellowmax import maximum_entropy_mellowmax
  from chainerrl.functions.mellowmax import mellowmax
label_desc: Use image node_id 4 for calling the TestMellowmax obj's underlying member method code with example usage: obj.test_forward_gpu() without return types