code: def forward_cpu(self, inputs, ratio, mask):
      (x,) = inputs
      if ratio == 0.0:
          y_expected = x
      else:
          y_expected = x * mask
      return (y_expected,)
  
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
label_desc: Use image node_id 2 for calling the TestDropout obj's underlying member method code with example usage: obj.forward_cpu(inputs, ratio, mask) and returns: y_expected