diff -r ca88bcfa5c15 Lib/idlelib/UndoDelegator.py
--- a/Lib/idlelib/UndoDelegator.py	Mon Jun 09 16:41:06 2014 -0400
+++ b/Lib/idlelib/UndoDelegator.py	Tue Jun 10 15:36:57 2014 +0530
@@ -361,5 +361,8 @@
     root.mainloop()
 
 if __name__ == "__main__":
+    import unittest
+    unittest.main('idlelib.idle_test.test_undodelegator', verbosity=2)
+
     from idlelib.idle_test.htest import run
     run(_undo_delegator)
diff -r ca88bcfa5c15 Lib/idlelib/idle_test/test_undodelegator.py
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/Lib/idlelib/idle_test/test_undodelegator.py	Tue Jun 10 15:36:57 2014 +0530
@@ -0,0 +1,131 @@
+"""Unittest for UndoDelegator in idlelib.UndoDelegator"""
+import unittest
+from unittest.mock import Mock
+from test.support import requires
+from idlelib.UndoDelegator import UndoDelegator
+from idlelib.Percolator import Percolator
+from tkinter import Text
+#from idlelib.idle_test.mock_tk import Text
+
+
+class UndoDelegatorTest(unittest.TestCase):
+
+    @classmethod
+    def setUpClass(cls):
+        requires('gui')
+        cls.text = Text()
+        cls.percolator = Percolator(cls.text)
+
+    @classmethod
+    def tearDownClass(cls):
+        cls.text.destroy()
+        del cls.text
+        del cls.percolator.redir
+        del cls.percolator
+
+    def setUp(self):
+        self.delegator = UndoDelegator()
+        self.percolator.insertfilter(self.delegator)
+        self.delegator.bell = Mock(wraps=self.delegator.bell)
+
+    def tearDown(self):
+        self.percolator.removefilter(self.delegator)
+        self.text.delete('1.0', 'end')
+        del self.delegator
+
+    def test_undo_event(self):
+        text = self.text
+
+        text.insert('insert', 'foobar')
+        text.insert('insert', 'h')
+        text.event_generate('<<undo>>')
+        self.assertEqual(text.get('1.0', 'end'), '\n')
+
+        text.insert('insert', 'foo')
+        text.insert('insert', 'bar')
+        text.delete('1.2', '1.4')
+        text.insert('insert', 'hello')
+        text.event_generate('<<undo>>')
+        self.assertEqual(text.get('1.0', '1.4'), 'foar')
+        text.event_generate('<<undo>>')
+        self.assertEqual(text.get('1.0', '1.6'), 'foobar')
+        text.event_generate('<<undo>>')
+        self.assertEqual(text.get('1.0', '1.3'), 'foo')
+        text.event_generate('<<undo>>')
+        self.delegator.undo_event('event')
+        self.assertTrue(self.delegator.bell.called)
+
+    def test_redo_event(self):
+        text = self.text
+
+        text.insert('insert', 'foo')
+        text.insert('insert', 'bar')
+        text.delete('1.0', '1.3')
+        text.event_generate('<<undo>>')
+        text.event_generate('<<redo>>')
+        self.assertEqual(text.get('1.0', '1.3'), 'bar')
+        text.event_generate('<<redo>>')
+        self.assertTrue(self.delegator.bell.called)
+
+    def test_dump_event(self):
+        """
+        Dump_event cannot be tested directly without changing
+        environment variables. So, test statements in dump_event
+        indirectly
+        """
+        text = self.text
+        d = self.delegator
+
+        text.insert('insert', 'foo')
+        text.insert('insert', 'bar')
+        text.delete('1.2', '1.4')
+        self.assertTupleEqual((d.pointer, d.can_merge), (3, True))
+        text.event_generate('<<undo>>')
+        self.assertTupleEqual((d.pointer, d.can_merge), (2, False))
+
+    def test_get_set_saved(self):
+        # test the getter method get_saved
+        # test the setter method set_saved
+        # indirectly test check_saved
+        d = self.delegator
+
+        self.assertTrue(d.get_saved())
+        self.text.insert('insert', 'a')
+        self.assertFalse(d.get_saved())
+        d.saved_change_hook = Mock()
+
+        d.set_saved(True)
+        self.assertEqual(d.pointer, d.saved)
+        self.assertTrue(d.saved_change_hook.called)
+
+        d.set_saved(False)
+        self.assertEqual(d.saved, -1)
+        self.assertTrue(d.saved_change_hook.called)
+
+    def test_undo_start_stop(self):
+        # test the undo_block_start and undo_block_stop methods
+        text = self.text
+
+        text.insert('insert', 'foo')
+        self.delegator.undo_block_start()
+        text.insert('insert', 'bar')
+        text.insert('insert', 'bar')
+        self.delegator.undo_block_stop()
+        self.assertEqual(text.get('1.0', '1.3'), 'foo')
+
+        # test another code path
+        self.delegator.undo_block_start()
+        text.insert('insert', 'bar')
+        self.delegator.undo_block_stop()
+        self.assertEqual(text.get('1.0', '1.3'), 'foo')
+
+    def test_addcmd(self):
+        text = self.text
+        # when number of undo operations exceeds max_undo
+        self.delegator.max_undo = max_undo = 10
+        for i in range(max_undo + 10):
+            text.insert('insert', 'foo')
+            self.assertLessEqual(len(self.delegator.undolist), max_undo)
+
+if __name__ == '__main__':
+    unittest.main(verbosity=2, exit=False)