code: def check_backward(self, c_data, h_data, x_data, y_grad):
      x = chainer.Variable(x_data)
      y = self._forward(self.link, x)
      c = self.link.c
      d = {"c_creator": c.creator, "y_creator": y.creator}
      y.grad = y_grad
      y.backward()
  
      def f():
          c_creator = d["c_creator"]
          y_creator = d["y_creator"]
          c, y = _zoneoutlstm(
              self.link, c_data, h_data, x_data, c_creator, y_creator
          )
          return (y,)
  
      (gx,) = gradient_check.numerical_grad(f, (x.data,), (y_grad,))
      testing.assert_allclose(gx, x.grad, atol=1e-3)
  
imports: import unittest
  import numpy
  import chainer
  from chainer import backend
  from chainer.backends import cuda
  from chainer import gradient_check
  from chainer import links
  from chainer import testing
  from chainer.testing import attr
label_desc: Use image node_id 7 for calling the TestZoneoutlstm obj's underlying member method code with example usage: obj.check_backward(c_data, h_data, x_data, y_grad) and returns: y