code: def testSingleFileLoading(self):
      self._WriteToFile("a", "abc")
      self.assertLoaderYields(["a", "b", "c"])
      self.assertLoaderYields([])
      self._WriteToFile("a", "xyz")
      self.assertLoaderYields(["x", "y", "z"])
      self.assertLoaderYields([])
  
imports: import functools
  import glob
  import os
  import shutil
  from unittest import mock
  import tensorflow
  from tensorboard.backend.event_processing import directory_loader
  from tensorboard.backend.event_processing import directory_watcher
  from tensorboard.backend.event_processing import event_file_loader
  from tensorboard.backend.event_processing import io_wrapper
  from tensorboard.util import test_util
label_desc: Use image node_id 6 for calling the DirectoryLoaderTest obj's underlying member method code with example usage: obj.testSingleFileLoading() without return types