code: def assert_tf_window(self, sampler):
      with self.cached_session() as sess:
          window = sess.run(sampler.pop_batch_op())
      self.assert_window(window)
  
imports: from __future__ import absolute_import, print_function
  import os
  import unittest
  import numpy
  import tensorflow
  from niftynet.engine.image_window import N_SPATIAL, LOCATION_FORMAT
  from niftynet.engine.image_window_dataset import ImageWindowDataset
  from niftynet.io.image_reader import ImageReader
  from tests.niftynet_testcase import NiftyNetTestCase
label_desc: Use image node_id 2 for calling the ImageWindowDataset_Generator_2D_Test obj's underlying member method code with example usage: obj.assert_tf_window(sampler) without return types