code: def test_custom_sentinel(self):
      i = iter_with_sleep()
      it = TimeoutIterator(i, timeout=0.5, sentinel="END")
      self.assertEqual(next(it), 1)
      self.assertEqual(next(it), "END")
  
      self.assertEqual(next(it), 2)
      self.assertEqual(next(it), 3)
      self.assertRaises(StopIteration, next, it)
  
imports: import unittest
  import time
  from iterators import TimeoutIterator
label_desc: Use image node_id 8 for calling the TestTimeoutIterator obj's underlying member method code with example usage: obj.test_custom_sentinel() without return types