diff -r e7ebf94629d2 Lib/idlelib/AutoExpand.py
--- a/Lib/idlelib/AutoExpand.py	Mon Jun 02 00:30:48 2014 +0100
+++ b/Lib/idlelib/AutoExpand.py	Mon Jun 02 19:45:08 2014 +0530
@@ -1,3 +1,8 @@
+"""Use AutoExpand to automatically complete the current word without
+having to type the entire word.
+AutoExpand searches for possible candidates in the text widget.
+If there is more than one, it cycles through all of them.
+"""
 import string
 import re
 
@@ -81,3 +86,9 @@
         while i > 0 and line[i-1] in self.wordchars:
             i = i-1
         return line[i:]
+
+if __name__ == '__main__':
+    from test import support; support.use_resources = ['gui']
+    import unittest
+    unittest.main('idlelib.idle_test.test_auto_expand',
+                   verbosity=2, exit=False)
diff -r e7ebf94629d2 Lib/idlelib/idle_test/test_auto_expand.py
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/Lib/idlelib/idle_test/test_auto_expand.py	Mon Jun 02 19:45:08 2014 +0530
@@ -0,0 +1,134 @@
+"""Unit tests for idlelib.AutoExpand"""
+import unittest
+#from idlelib.idle_test.mock_tk import Text
+from test.support import requires
+from tkinter import Text
+from idlelib.AutoExpand import AutoExpand
+
+Expand = AutoExpand
+
+
+class Dummy_Editwin:
+    """
+    Mock editor window class
+    """
+
+    def __init__(self, text):
+        self.text = text
+
+
+class AutoExpandTest(unittest.TestCase):
+
+    @classmethod
+    def setUpClass(cls):
+        requires('gui')
+        cls.text = Text()
+        cls.editwin = Dummy_Editwin(cls.text)
+        cls.auto_expand = Expand(cls.editwin)
+
+    @classmethod
+    def tearDownClass(cls):
+        cls.text.destroy()
+        del cls.text
+
+    def tearDown(self):
+        self.text.delete('1.0', 'end')
+
+    def test_get_prevword(self):
+        text = self.editwin.text
+        previous = self.auto_expand.getprevword
+        equal = self.assertEqual
+
+        equal(previous(), '')
+
+        text.insert('insert', 't')
+        equal(previous(), 't')
+
+        text.insert('insert', 'his')
+        equal(previous(), 'this')
+
+        text.insert('insert', ' ')
+        equal(previous(), '')
+
+        text.insert('insert', 'is')
+        equal(previous(), 'is')
+
+        text.insert('insert', '\nsample\nstring')
+        equal(previous(), 'string')
+
+        text.delete('3.0', 'insert')
+        equal(previous(), '')
+
+        text.delete('1.0', 'end')
+        equal(previous(), '')
+
+    def test_get_words(self):
+        text = self.editwin.text
+        words = self.auto_expand.getwords
+        equal = self.assertCountEqual
+
+        def delete_all():
+            text.delete('1.0', 'end')
+
+        equal(words(), [])
+
+        text.insert('insert', 'a ab')
+        equal(words(), [])
+        delete_all()
+
+        text.insert('insert', 'ab a')
+        equal(words(), ['ab', 'a'])
+        delete_all()
+
+        text.insert('insert', 'aab aba\n acb\n')
+        text.insert('insert', 'a')
+        equal(words(), ['aab', 'aba', 'acb', 'a'])
+        text.insert('insert', 'a')
+        equal(words(), ['aab', 'aa'])
+        text.insert('insert', 'b')
+        equal(words(), [])
+        delete_all()
+
+        text.insert('insert', 'a\nb\nc\nd')
+        text.insert('insert', 'abc')
+        equal(words(), [])
+
+    def test_expand_event(self):
+        text = self.editwin.text
+        expand = self.auto_expand.expand_word_event
+        previous = self.auto_expand.getprevword
+        equal = self.assertEqual
+
+        expand('event')
+        equal(previous(), '')
+
+        text.insert('insert', 'abc a')
+        expand('event')
+        equal(previous(), 'abc')
+
+        text.insert('insert', 'b ac ad a')
+        expand('event')
+        equal(previous(), 'ad')
+        expand('event')
+        equal(previous(), 'ac')
+
+        text.insert('insert', '\na')
+        text.insert('insert', ' eab')
+        expand('event')
+        equal(previous(), 'eab')
+
+        text.delete('1.0', 'end')
+
+        text.insert('insert', 'a\n \nab abc abcd \na')
+        expand('event')
+        equal(previous(), 'abcd')
+        expand('event')
+        equal(previous(), 'abc')
+        expand('event')
+        equal(previous(), 'ab')
+        expand('event')
+        equal(previous(), 'a')
+
+
+if __name__ == '__main__':
+    unittest.main(verbosity=2, exit=2)