code: def test_3d_idw_symmetric(self):
      self._test_grads_images("idw", "symmetric", ndim=3)
  
imports: from __future__ import absolute_import, print_function, division
  import base64
  import numpy
  import tensorflow
  from niftynet.layer.grid_warper import AffineGridWarperLayer
  from niftynet.layer.resampler import ResamplerLayer
  from tests.niftynet_testcase import NiftyNetTestCase
label_desc: Use image node_id 13 for calling the image_test obj's underlying member method code with example usage: obj.test_3d_idw_symmetric() without return types