code: def _train(self):
      net_run_with_sys_argv(
          [
              "net_run",
              "-a",
              self.application,
              "-c",
              self.config,
              "train",
              "--max_iter",
              "2",
          ]
      )
      checkpoint = os.path.join(
          MODEL_HOME,
          "models",
          self.location,
          "models",
          "model.ckpt-2.index",
      )
      self.assertTrue(
          os.path.exists(checkpoint),
          "Expected {} to exist.".format(checkpoint),
      )
  
imports: from __future__ import absolute_import
  from __future__ import division
  from __future__ import print_function
  import os, sys, unittest
  import tensorflow
  from niftynet.utilities.download import download
  from niftynet.utilities.niftynet_global_config import NiftyNetGlobalConfig
  from niftynet import main
  from niftynet.application.base_application import SingletonApplication
  from tests.niftynet_testcase import NiftyNetTestCase
label_desc: Use image node_id 3 for calling the DenseVNetAbdominalCTModelZooTest obj's underlying member method code with example usage: obj._train() without return types