diff -r c64216addd7f Lib/codecs.py
--- a/Lib/codecs.py	Mon Aug 22 11:55:57 2011 +1000
+++ b/Lib/codecs.py	Mon Aug 22 15:22:49 2011 +1000
@@ -308,6 +308,7 @@
 
     def getstate(self):
         # additional state info is always 0
+        # After a reset, the state must be buffer == b""
         return (self.buffer, 0)
 
     def setstate(self, state):
diff -r c64216addd7f Lib/test/test_codecs.py
--- a/Lib/test/test_codecs.py	Mon Aug 22 11:55:57 2011 +1000
+++ b/Lib/test/test_codecs.py	Mon Aug 22 15:22:49 2011 +1000
@@ -2,7 +2,10 @@
 import unittest
 import codecs
 import locale
-import sys, _testcapi, io
+import sys
+import _testcapi
+import io
+
 
 class Queue(object):
     """
@@ -15,7 +18,7 @@
         self._buffer += chars
 
     def read(self, size=-1):
-        if size<0:
+        if size < 0:
             s = self._buffer
             self._buffer = self._buffer[:0] # make empty
             return s
@@ -24,9 +27,39 @@
             self._buffer = self._buffer[size:]
             return s
 
+
+class BufferedCodecsTest(unittest.TestCase):
+    # Note, this does not exhaustively test the code. The code is exercised
+    # during unit testing by other modules which are subclassing Buffered
+    # coders. It tests some of the non-abstract logic included in this base
+    # class.
+
+    def test_base_decoder(self):
+        dec = codecs.BufferedIncrementalDecoder()
+        with self.assertRaises(NotImplementedError):
+            dec._buffer_decode(1, 2, 3)
+
+    def test_base_encoder(self):
+
+        class TestEncoder(codecs.BufferedIncrementalEncoder):
+            def _buffer_encode(self, input, errors, final):
+                return 0, 7
+
+        enc = TestEncoder()
+
+        enc.encode("Hello, world!")
+        self.assertEqual(enc.getstate(), "world!")
+
+        enc.setstate("Hello, world!")
+        self.assertEqual(enc.getstate(), "Hello, world!")
+
+        enc.reset()
+        self.assertEqual(enc.getstate(), 0)
+
+
 class MixInCheckStateHandling:
     def check_state_handling_decode(self, encoding, u, s):
-        for i in range(len(s)+1):
+        for i in range(len(s) + 1):
             d = codecs.getincrementaldecoder(encoding)()
             part1 = d.decode(s[:i])
             state = d.getstate()
@@ -45,17 +78,18 @@
             d = codecs.getincrementaldecoder(encoding)()
             d.setstate(state)
             part2 = d.decode(s[i:], True)
-            self.assertEqual(u, part1+part2)
+            self.assertEqual(u, part1 + part2)
 
     def check_state_handling_encode(self, encoding, u, s):
-        for i in range(len(u)+1):
+        for i in range(len(u) + 1):
             d = codecs.getincrementalencoder(encoding)()
             part1 = d.encode(u[:i])
             state = d.getstate()
             d = codecs.getincrementalencoder(encoding)()
             d.setstate(state)
             part2 = d.encode(u[i:], True)
-            self.assertEqual(s, part1+part2)
+            self.assertEqual(s, part1 + part2)
+
 
 class ReadTest(unittest.TestCase, MixInCheckStateHandling):
     def check_partial(self, input, partialresults):
@@ -66,7 +100,8 @@
         q = Queue(b"")
         r = codecs.getreader(self.encoding)(q)
         result = ""
-        for (c, partialresult) in zip(input.encode(self.encoding), partialresults):
+        for (c, partialresult) in zip(input.encode(self.encoding),
+                                      partialresults):
             q.write(bytes([c]))
             result += r.read()
             self.assertEqual(result, partialresult)
@@ -77,7 +112,8 @@
         # do the check again, this time using a incremental decoder
         d = codecs.getincrementaldecoder(self.encoding)()
         result = ""
-        for (c, partialresult) in zip(input.encode(self.encoding), partialresults):
+        for (c, partialresult) in zip(input.encode(self.encoding),
+                                      partialresults):
             result += d.decode(bytes([c]))
             self.assertEqual(result, partialresult)
         # check that there's nothing left in the buffers
@@ -87,7 +123,8 @@
         # Check whether the reset method works properly
         d.reset()
         result = ""
-        for (c, partialresult) in zip(input.encode(self.encoding), partialresults):
+        for (c, partialresult) in zip(input.encode(self.encoding),
+                                      partialresults):
             result += d.decode(bytes([c]))
             self.assertEqual(result, partialresult)
         # check that there's nothing left in the buffers
@@ -96,10 +133,9 @@
 
         # check iterdecode()
         encoded = input.encode(self.encoding)
-        self.assertEqual(
-            input,
-            "".join(codecs.iterdecode([bytes([c]) for c in encoded], self.encoding))
-        )
+        self.assertEqual(input,
+                       "".join(codecs.iterdecode([bytes([c]) for c in encoded],
+                                                 self.encoding)))
 
     def test_readline(self):
         def getreader(input):
@@ -128,27 +164,28 @@
         vw = []
         vwo = []
         for (i, lineend) in enumerate("\n \r\n \r \u2028".split()):
-            vw.append((i*200)*"\3042" + lineend)
-            vwo.append((i*200)*"\3042")
+            vw.append((i * 200) * "\3042" + lineend)
+            vwo.append((i * 200) * "\3042")
         self.assertEqual(readalllines("".join(vw), True), "".join(vw))
-        self.assertEqual(readalllines("".join(vw), False),"".join(vwo))
+        self.assertEqual(readalllines("".join(vw), False), "".join(vwo))
 
         # Test lines where the first read might end with \r, so the
         # reader has to look ahead whether this is a lone \r or a \r\n
         for size in range(80):
             for lineend in "\n \r\n \r \u2028".split():
-                s = 10*(size*"a" + lineend + "xxx\n")
+                s = 10 * (size * "a" + lineend + "xxx\n")
                 reader = getreader(s)
                 for i in range(10):
                     self.assertEqual(
                         reader.readline(keepends=True),
-                        size*"a" + lineend,
+                        size * "a" + lineend,
                     )
+
                 reader = getreader(s)
                 for i in range(10):
                     self.assertEqual(
                         reader.readline(keepends=False),
-                        size*"a",
+                        size * "a",
                     )
 
     def test_bug1175396(self):
@@ -1760,6 +1797,7 @@
         SurrogateEscapeTest,
         BomTest,
         TransformCodecTest,
+        BufferedCodecsTest,
     )
 
 
diff -r c64216addd7f Misc/NEWS
--- a/Misc/NEWS	Mon Aug 22 11:55:57 2011 +1000
+++ b/Misc/NEWS	Mon Aug 22 15:22:49 2011 +1000
@@ -1209,6 +1209,9 @@
 Tests
 -----
 
+- Issue #12808: Add unit tests for the BufferedIncrementalEncoder/Decoder
+  base classes (initial patch by Tennessee Leeuwenburg)
+
 - Issue #11651: Improve the Makefile test targets to run more of the test suite
   more quickly. The --multiprocess option is now enabled by default, reducing
   the amount of time needed to run the tests. "make test" and "make quicktest"