code: def test_hooks(self):
      w_pre = np.copy(self.target.w.data)
      h_pre = WeightSaveHook()
      h_post = WeightSaveHook()
      self.create()
      self.optimizer.add_hook(h_pre, timing="pre")
      self.optimizer.add_hook(
          h_post, name="WeightSaveHookPost", timing="post"
      )
  
      x = chainer.Variable(np.array(5.0, dtype=np.float32))
      self.optimizer.update(self.target, x)
      w_post = np.copy(self.target.w.data)
  
      self.assertEqual(w_pre, h_pre.value)
      self.assertEqual(w_post, h_post.value)
      self.assertNotEqual(h_pre.value, h_post.value)
  
imports: import pickle
  import unittest
  import numpy
  import six
  import chainer
  from chainer import functions
  from chainer import optimizers
  from chainer import testing
label_desc: Use image node_id 4 for calling the TestOptimizerHooks obj's underlying member method code with example usage: obj.test_hooks() without return types