diff -r a0e8f2d882a3 Lib/idlelib/Percolator.py
--- a/Lib/idlelib/Percolator.py	Mon Jun 30 20:00:03 2014 -0400
+++ b/Lib/idlelib/Percolator.py	Tue Jul 08 19:48:41 2014 +0530
@@ -100,5 +100,9 @@
     root.mainloop()
 
 if __name__ == "__main__":
+    import unittest
+    unittest.main('idlelib.idle_test.test_percolator', verbosity=2,
+                  exit=False)
+
     from idlelib.idle_test.htest import run
     run(_percolator)
diff -r a0e8f2d882a3 Lib/idlelib/idle_test/test_percolator.py
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/Lib/idlelib/idle_test/test_percolator.py	Tue Jul 08 19:48:41 2014 +0530
@@ -0,0 +1,89 @@
+import unittest
+from test.support import requires
+from tkinter import Text, Tk
+from idlelib.Percolator import Percolator, Delegator
+
+class MyFilter(Delegator):
+    def __init__(self):
+        Delegator.__init__(self, None)
+
+    def insert(self, *args):
+        self.delegate.insert(*args)
+
+    def delete(self, *args):
+        self.delegate.delete(*args)
+
+class PercolatorTest(unittest.TestCase):
+
+    @classmethod
+    def setUpClass(cls):
+        requires('gui')
+        cls.root = Tk()
+        cls.text = Text(cls.root)
+
+    @classmethod
+    def tearDownClass(cls):
+        cls.text.destroy()
+        cls.root.destroy()
+
+    def setUp(self):
+        self.percolator = Percolator(self.text)
+        self.filter_one = MyFilter()
+        self.filter_two = MyFilter()
+
+    def tearDown(self):
+        self.percolator.close()
+        self.text.delete('1.0', 'end')
+
+    def test_insertfilter(self):
+        with self.assertRaises(AssertionError) as ae:
+            self.percolator.insertfilter('filter')
+        self.filter_two.delegate = ''
+        with self.assertRaises(AssertionError) as ae:
+            self.percolator.insertfilter(self.filter_two)
+
+        self.assertIsNone(self.filter_one.delegate)
+        self.percolator.insertfilter(self.filter_one)
+        self.assertIsNotNone(self.filter_one.delegate)
+        self.assertEqual(self.percolator.top, self.filter_one)
+
+    def test_removefilter(self):
+        with self.assertRaises(AssertionError) as ae:
+            self.percolator.removefilter('filter')
+        self.filter_two.delegate = None
+        with self.assertRaises(AssertionError) as ae:
+            self.percolator.removefilter(self.filter_two)
+
+        filter_three = MyFilter()
+        self.percolator.insertfilter(self.filter_one)
+        self.percolator.insertfilter(self.filter_two)
+        self.percolator.removefilter(self.filter_two)
+        self.assertEqual(self.percolator.top, self.filter_one)
+        self.assertIsNone(self.filter_two.delegate)
+
+        filter_three.delegate = ''
+        with self.assertRaises(AssertionError) as ae:
+            self.percolator.removefilter(filter_three)
+
+        filter_three = MyFilter()
+        self.percolator.insertfilter(self.filter_two)
+        self.percolator.insertfilter(filter_three)
+        self.percolator.removefilter(self.filter_one)
+        self.assertEqual(self.percolator.top, filter_three)
+        self.assertEqual(filter_three.delegate, self.filter_two)
+        self.assertEqual(self.filter_two.delegate, self.percolator.bottom)
+        self.assertIsNone(self.filter_one.delegate)
+
+    def test_insert(self):
+        self.percolator.insertfilter(self.filter_one)
+        self.text.insert('insert', 'foo')
+        self.assertEqual(self.text.get('1.0', 'end'), 'foo\n')
+
+    def test_delete(self):
+        self.percolator.insertfilter(self.filter_one)
+        self.text.insert('insert', 'foo')
+        self.text.delete('1.0', '1.2')
+        self.assertEqual(self.text.get('1.0', 'end'), 'o\n')
+
+if __name__ == '__main__':
+    unittest.main(verbosity=2)