docstr: Test whether forward and backward can work properly.
docstr_tok: ["Test","whether","forward","and","backward","can","work","properly","."]
code: def assert_forward_backward(self, model, input_data):
      """
      Test whether forward and backward can work properly.
      """
      output = model.forward(input_data)
      grad_input = model.backward(input_data, output)
  
imports: from __future__ import print_function
  import logging
  import shutil
  from unittest import TestCase
  import keras.backend
  from bigdl.dllib.nncontext import *
  from bigdl.dllib.feature.image import ImageSet
label_desc: Use image node_id 9 for calling the ZooTestCase obj's underlying member method code with example usage: obj.assert_forward_backward(model, input_data) without return types