code: def test_variable_grad(self):
      x = numpy.random.uniform(-1, 1, (3, 2)).astype(numpy.float32)
      x = variable.Variable(x)
      w = numpy.random.uniform(-1, 1, (3, 2)).astype(numpy.float32)
      w = variable.Variable(w)
  
      y = functions.forget(lambda a, b: a + b, x, w)
      y.grad_var = variable.Variable(numpy.ones_like(y.data))
      y.backward()
  
      assert isinstance(x.grad_var, variable.Variable)
      assert isinstance(w.grad_var, variable.Variable)
  
imports: import functools
  import unittest
  import numpy
  import six
  import chainer
  from chainer import cuda
  from chainer import functions
  from chainer import gradient_check
  from chainer import links
  from chainer import testing
  from chainer.testing import attr
  from chainer import variable
label_desc: Use image node_id 1 for calling the TestForgetGrad obj's underlying member method code with example usage: obj.test_variable_grad() without return types