code: def check_weight_decay(self, backend_configs):
      target = self.target
      assert len(backend_configs) == len(list(target.params()))
      devices = [bc.device for bc in backend_configs]
  
      decay = 0.2
  
      # Compute expected
      expects = []
      for param, device in zip(target.params(), devices):
          expects.append(param.array - param.grad - decay * param.array)
          param.to_device(device)
  
      opt = optimizers.SGD(lr=1)
      opt.setup(self.target)
      opt.add_hook(optimizer_hooks.WeightDecay(decay))
      opt.update()
  
      # Validate
      for expect, param in zip(expects, target.params()):
          testing.assert_allclose(expect, param.array)
  
file_path: chainer/tests/chainer_tests/optimizer_hooks_tests/test_weight_decay.py
imports: import unittest
  import numpy
  import chainer
  import chainer.functions
  from chainer import optimizer_hooks
  from chainer import optimizers
  from chainer import testing
  import utils
label_desc: Use image node_id 2 for calling the TestWeightDecay obj's underlying member method code with example usage: obj.check_weight_decay(backend_configs) without return types