diff --git a/Data/Encoding/Base.hs b/Data/Encoding/Base.hs
index bc7223a..ae3f7e7 100644
--- a/Data/Encoding/Base.hs
+++ b/Data/Encoding/Base.hs
@@ -114,7 +114,7 @@ data EncodeState
 data EncodingException
 	= HasNoRepresentation Char	-- ^ Thrown if a specific character
 					--   is not representable in an encoding.
-	deriving (Show,Typeable)
+	deriving (Eq,Show,Typeable)
 
 -- | This exception type is thrown whenever something went wrong during the
 --   decoding-process.
diff --git a/Test/Tester.hs b/Test/Tester.hs
new file mode 100644
index 0000000..35cf58d
--- /dev/null
+++ b/Test/Tester.hs
@@ -0,0 +1,37 @@
+{-# LANGUAGE ExistentialQuantification #-}
+module Test.Tester where
+
+import Data.Encoding
+import Test.HUnit
+import Data.Word
+import Data.ByteString (pack)
+import Control.Exception (catchDyn,evaluate)
+
+data EncodingTest
+	= forall enc. (Encoding enc,Show enc) =>
+		EncodingTest enc String [Word8]
+	| forall enc. (Encoding enc,Show enc) =>
+		DecodingError enc [Word8] DecodingException
+
+instance Testable EncodingTest where
+	test (EncodingTest enc src trg) = TestList
+		[TestLabel (show enc ++ " encodable")
+			(TestCase $ (all (encodable enc) src) @=? True)
+		,TestLabel (show enc ++ " encoding")
+			(TestCase $ (encode enc src) @=? bstr)
+		,TestLabel (show enc ++ " decodable")
+			(TestCase $ (decodable enc bstr) @=? True)
+		,TestLabel (show enc ++ " decoding")
+			(TestCase $ (decode enc bstr) @=? src)
+		]
+		where
+		bstr = pack trg
+	test (DecodingError enc trg what) = TestList
+		[TestLabel (show enc ++ " not decodable") $
+			TestCase $ assert $ not $ decodable enc (pack trg)
+		,TestLabel (show enc ++ " decoding error") $ TestCase $ 
+			catchDyn (do
+				evaluate (decode enc (pack trg) == "")
+				return ())
+				(\exc -> exc @=? what)
+		]