code: def _run_trainer(self, extension, expect, optimizer=None):
      if optimizer is None:
          optimizer = self.optimizer
      extension.initialize(self.trainer)
  
      actual = []
      for _ in expect:
          self.trainer.updater.update()
          actual.append(optimizer.x)
          if self.trigger(self.trainer):
              extension(self.trainer)
  
      self.assertEqual(actual, expect)
  
file_path: chainer/tests/chainer_tests/training_tests/extensions_tests/test_polynomial_shift.py
imports: import unittest
  import mock
  from chainer import testing
  from chainer.training import extensions
  from chainer.training import util
label_desc: Use image node_id 2 for calling the TestPolynomialShift obj's underlying member method code with example usage: obj._run_trainer(extension, expect, optimizer) without return types