text: #!/usr/bin/env python
  
  import unittest
  import time
  
  from tornado.testing import AsyncTestCase, LogTrapTestCase
  
  class TestIOLoop(AsyncTestCase, LogTrapTestCase):
      def test_add_callback_wakeup(self):
          # Make sure that add_callback from inside a running IOLoop
          # wakes up the IOLoop immediately instead of waiting for a timeout.
          def callback():
              self.called = True
              self.stop()
  
          def schedule_callback():
              self.called = False
              self.io_loop.add_callback(callback)
              # Store away the time so we can check if we woke up immediately
              self.start_time = time.time()
          self.io_loop.add_timeout(time.time(), schedule_callback)
          self.wait()
          self.assertAlmostEqual(time.time(), self.start_time, places=2)
          self.assertTrue(self.called)
  
  if __name__ == "__main__":
      unittest.main()
  