code: def testRelu6GradGrad(self):
      inputs = constant_op.constant(
          [[-2, -1, 1, 3], [5, 7, 8, 9]], dtype=dtypes.float32
      )
      x_init_value = np.array([[-3.5, -1.5, 2, 4], [4.5, 7.5, 8.5, 11]])
      r = nn_ops.relu6(inputs)
      r_g = gradients_impl.gradients(r, inputs)[0]
      with self.cached_session():
          error = gradient_checker.compute_gradient_error(
              inputs,
              inputs.get_shape().as_list(),
              r_g,
              r_g.get_shape().as_list(),
              x_init_value=x_init_value,
          )
          self.assertLess(error, 1e-4)
  
imports: import numpy
  from tensorflow.python.eager import backprop
  from tensorflow.python.framework import constant_op
  from tensorflow.python.framework import dtypes
  from tensorflow.python.framework import test_util
  from tensorflow.python.ops import array_ops
  from tensorflow.python.ops import gen_nn_ops
  from tensorflow.python.ops import gradient_checker
  from tensorflow.python.ops import gradient_checker_v2
  from tensorflow.python.ops import gradients_impl
  from tensorflow.python.ops import nn_grad
  from tensorflow.python.ops import nn_impl
  from tensorflow.python.ops import nn_ops
  from tensorflow.python.platform import test
label_desc: Use image node_id 1 for calling the Relu6OpTest obj's underlying member method code with example usage: obj.testRelu6GradGrad() without return types