code: def tearDown(self):
      # Set None to delete cuda array
      self.f = None
      self.y1 = None
      self.y2 = None
      self.gx1 = None
  
imports: import unittest
  import mock
  import numpy
  import six
  import chainer
  from chainer import _backprop_utils
  from chainer.backends import cuda
  from chainer import testing
  from chainer.testing import attr
label_desc: Use image node_id 3 for calling the TestFunctionNode obj's underlying member method code with example usage: obj.tearDown() without return types