code: def setUp(self):
      self.optimizer = mock.MagicMock()
      self.extension = extensions.WarmupShift(
          "x",
          self.warmup_start,
          self.warmup_iter,
          self.init,
          self.optimizer,
      )
  
      self.interval = 1
      self.expect = [
          e for e in self.expect for _ in range(self.interval)
      ]
      self.trigger = util.get_trigger((self.interval, "iteration"))
  
      self.trainer = testing.get_trainer_with_mock_updater(self.trigger)
      self.trainer.updater.get_optimizer.return_value = self.optimizer
  
file_path: chainer/tests/chainer_tests/training_tests/extensions_tests/test_warmup_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 1 for calling the TestWarmupShift obj's underlying member method code with example usage: obj.setUp() without return types