code: def test_remove_stale_snapshots(self):
      fmt = "snapshot_iter_{.updater.iteration}"
      retain = 3
      snapshot = extensions.snapshot(
          filename=fmt, n_retains=retain, autoload=False
      )
  
      trainer = testing.get_trainer_with_mock_updater()
      trainer.out = self.path
      trainer.extend(snapshot, trigger=(1, "iteration"), priority=2)
  
      class TimeStampUpdater:
          t = time.time() - 100
          name = "ts_updater"
          priority = 1  # This must be called after snapshot taken
  
          def __call__(self, _trainer):
              filename = os.path.join(
                  _trainer.out, fmt.format(_trainer)
              )
              self.t += 1
              # For filesystems that does low timestamp precision
              os.utime(filename, (self.t, self.t))
  
      trainer.extend(TimeStampUpdater(), trigger=(1, "iteration"))
      trainer.run()
      assert 10 == trainer.updater.iteration
      assert trainer._done
  
      pattern = os.path.join(trainer.out, "snapshot_iter_*")
      found = [os.path.basename(path) for path in glob.glob(pattern)]
      assert retain == len(found)
      found.sort()
      # snapshot_iter_(8, 9, 10) expected
      expected = ["snapshot_iter_{}".format(i) for i in range(8, 11)]
      expected.sort()
      assert expected == found
  
      trainer2 = testing.get_trainer_with_mock_updater()
      trainer2.out = self.path
      assert not trainer2._done
      snapshot2 = extensions.snapshot(filename=fmt, autoload=True)
      # Just making sure no error occurs
      snapshot2.initialize(trainer2)
  
imports: import glob
  import itertools
  import os
  import shutil
  import tempfile
  import time
  import unittest
  import mock
  import pytest
  from chainer import testing
  from chainer import training
  from chainer.training import extensions
  from chainer.training.extensions._snapshot import _find_latest_snapshot
  from chainer.training.extensions._snapshot import _find_snapshot_files
  from chainer.training.extensions._snapshot import _find_stale_snapshots
label_desc: Use image node_id 3 for calling the TestRemoveStaleSnapshots obj's underlying member method code with example usage: obj.test_remove_stale_snapshots() without return types