diff --git a/System/Hardware/Serialport/Posix.hsc b/System/Hardware/Serialport/Posix.hsc
--- a/System/Hardware/Serialport/Posix.hsc
+++ b/System/Hardware/Serialport/Posix.hsc
@@ -8,7 +8,7 @@
 import System.Posix.Types
 import System.Posix.Terminal
 import System.Hardware.Serialport.Types
-import Foreign
+import Foreign (Ptr, castPtr, alloca, peek, with)
 import Foreign.C
 import GHC.IO.Handle
 import GHC.IO.Device
@@ -16,6 +16,8 @@
 import Data.Typeable
 import GHC.IO.Buffer
 import GHC.IO.Encoding
+import Control.Monad (void)
+import Data.Bits
 
 
 data SerialPort = SerialPort {
@@ -28,7 +30,7 @@
 instance RawIO SerialPort where
   read (SerialPort fd' _) ptr n = return . fromIntegral =<< fdReadBuf fd' ptr (fromIntegral n)
   readNonBlocking _ _ _ = error "readNonBlocking not implemented"
-  write (SerialPort fd' _) ptr n = fdWriteBuf fd' ptr (fromIntegral n) >> return ()
+  write (SerialPort fd' _) ptr n = void (fdWriteBuf fd' ptr (fromIntegral n))
   writeNonBlocking _ _ _ = error "writenonblocking not implemented"
 
 
@@ -76,16 +78,27 @@
   return =<< setSerialSettings serial_port settings
 
 
+-- |Use specific encoding for an action and restore old encoding afterwards
+withEncoding :: TextEncoding -> IO a -> IO a
+#if MIN_VERSION_base(4,5,0)
+withEncoding encoding fun = do
+  cur_enc <- getForeignEncoding
+  setForeignEncoding encoding
+  result <- fun
+  setForeignEncoding cur_enc
+  return result
+#else
+withEncoding _ fun = fun
+#endif
+
+
 -- |Receive bytes, given the maximum number
 recv :: SerialPort -> Int -> IO B.ByteString
 recv (SerialPort fd' _) n = do
-  cur_enc <- getForeignEncoding
-  setForeignEncoding char8
-  result <- Ex.try $ fdRead fd' count :: IO (Either IOError (String, ByteCount))
-  setForeignEncoding cur_enc
-  return $ case result of
-             Right (str, _) -> B.pack str
-             Left _         -> B.empty
+  result <- withEncoding char8 $ Ex.try $ fdRead fd' count :: IO (Either IOError (String, ByteCount))
+  case result of
+     Right (str, _) -> return $ B.pack str
+     Left _         -> return B.empty
   where
     count = fromIntegral n
 
@@ -95,10 +108,7 @@
         -> B.ByteString
         -> IO Int          -- ^ Number of bytes actually sent
 send (SerialPort fd' _ ) msg = do
-  cur_enc <- getForeignEncoding
-  setForeignEncoding char8
-  ret <- fdWrite fd' (B.unpack msg)
-  setForeignEncoding cur_enc
+  ret <- withEncoding char8 (fdWrite fd' (B.unpack msg))
   return $ fromIntegral ret
 
 
diff --git a/System/Hardware/Serialport/Types.hs b/System/Hardware/Serialport/Types.hs
--- a/System/Hardware/Serialport/Types.hs
+++ b/System/Hardware/Serialport/Types.hs
@@ -17,12 +17,12 @@
   | CS38400
   | CS57600
   | CS115200
-  deriving (Show)
+  deriving (Show, Eq, Bounded)
 
 
-data StopBits = One | Two
-data Parity = Even | Odd | NoParity
-data FlowControl = Software | NoFlowControl
+data StopBits = One | Two deriving (Show, Eq, Bounded)
+data Parity = Even | Odd | NoParity deriving (Show, Eq, Bounded)
+data FlowControl = Software | NoFlowControl deriving (Show, Eq, Bounded)
 
 data SerialPortSettings = SerialPortSettings {
                       commSpeed    :: CommSpeed,   -- ^ baudrate
diff --git a/System/Hardware/Serialport/Windows.hs b/System/Hardware/Serialport/Windows.hs
--- a/System/Hardware/Serialport/Windows.hs
+++ b/System/Hardware/Serialport/Windows.hs
@@ -28,7 +28,7 @@
 instance RawIO SerialPort where
   read (SerialPort h _) ptr n = return . fromIntegral =<< win32_ReadFile h ptr (fromIntegral n) Nothing
   readNonBlocking _ _ _ = error "readNonBlocking not implemented"
-  write (SerialPort h _) ptr n = win32_WriteFile h ptr (fromIntegral n) Nothing >> return ()
+  write (SerialPort h _) ptr n = void (win32_WriteFile h ptr (fromIntegral n) Nothing)
   writeNonBlocking _ _ _ = error "writenonblocking not implemented"
 
 
diff --git a/serialport.cabal b/serialport.cabal
--- a/serialport.cabal
+++ b/serialport.cabal
@@ -1,7 +1,7 @@
 Name:           serialport
-Version:        0.4.5
-Cabal-Version:  >= 1.6
-Build-Type:     Custom
+Version:        0.4.6
+Cabal-Version:  >= 1.8
+Build-Type:     Simple
 license:        BSD3
 license-file:   LICENSE
 copyright:      (c) 2009-2011 Joris Putcuyps
@@ -30,3 +30,12 @@
     Build-Depends:    Win32
     Other-Modules:    System.Hardware.Serialport.Windows
                       System.Win32.Comm
+
+Test-Suite Tests
+  type:               exitcode-stdio-1.0
+  main-is:            Tests.hs
+  hs-source-dirs:     tests
+  build-depends:      base,
+                      HUnit,
+                      bytestring,
+                      serialport
diff --git a/tests/Tests.hs b/tests/Tests.hs
new file mode 100644
--- /dev/null
+++ b/tests/Tests.hs
@@ -0,0 +1,110 @@
+import System.Environment
+import System.Hardware.Serialport
+import System.IO
+import qualified Data.ByteString.Char8 as B
+import Test.HUnit
+import System.Exit
+import Control.Concurrent
+
+
+
+configureComm :: SerialPort -> CommSpeed -> IO ()
+configureComm h cs = do
+  let control_char = case cs of
+        CS1200   -> "a"
+        CS2400   -> "b"
+        CS4800   -> "c"
+        CS9600   -> "d"
+        CS19200  -> "e"
+        CS57600  -> "f"
+        CS115200 -> "g"
+        _        -> error "commSpeed not supported"
+  send h $ B.pack control_char
+  assertEqual "configure serial port" control_char . B.unpack =<< recv h 100
+
+
+
+sendRange :: SerialPort -> IO ()
+sendRange s =
+  mapM_ sendAndRecv ['\x00'..'\xff']
+  where
+    sendAndRecv :: Char -> IO ()
+    sendAndRecv c = do
+      send s $ B.pack [c]
+      assertEqual "byte mismatch" [c] . B.unpack =<< recv s 1
+
+
+
+testSerialport :: CommSpeed -> String -> SerialPort -> Test
+testSerialport cs test_port control = TestCase $ do
+  configureComm control cs
+  withSerial test_port defaultSerialSettings { commSpeed = cs } sendRange
+  assertEqual "test ok" "ok\r\n" . B.unpack =<< recv control 100
+
+
+
+sendRangeH :: Handle -> IO ()
+sendRangeH h =
+  mapM_ sendAndRecv ['\x00'..'\xff']
+  where
+    sendAndRecv :: Char -> IO ()
+    sendAndRecv c = do
+      hPutChar h c
+      assertEqual "byte mismatch" c =<< hGetChar h
+
+
+
+testHandle :: CommSpeed -> String -> SerialPort -> Test
+testHandle cs test_port control = TestCase $ do
+  configureComm control cs
+  h <- hOpenSerial test_port defaultSerialSettings { commSpeed = cs }
+  sendRangeH h
+  hClose h
+  assertEqual "test ok" "ok\r\n" . B.unpack =<< recv control 100
+
+
+testDelay :: String -> SerialPort -> Test
+testDelay test_port control = TestCase $ do
+  s <- openSerial test_port defaultSerialSettings { timeout = 6 }
+  let control_char = 'h'
+  send control $ B.pack [control_char]
+  assertEqual "configure serial port" [control_char] . B.unpack =<< recv control 100
+
+  send s $ B.pack "a"
+  assertEqual "immediatly" "aA" . B.unpack =<< recv s 10
+
+  send s $ B.pack "b"
+  assertEqual "delay 50 ms" "bB" . B.unpack =<< recv s 10
+
+  send s $ B.pack "c"
+  assertEqual "delay 150 ms" "c" . B.unpack =<< recv s 10
+  assertEqual "second try" "C" . B.unpack =<< recv s 10
+
+  closeSerial s
+
+
+
+tests :: String -> SerialPort -> Test
+tests test_port control = TestList $ map (\(descr,fun) -> TestLabel descr (fun test_port control)) testCases
+  where
+    testCases = [
+      ("b1200 Serialport",  testSerialport CS1200),
+      ("b2400 Serialport",  testSerialport CS2400),
+      ("b4800 Serialport",  testSerialport CS4800),
+      ("b9600 Serialport",  testSerialport CS9600),
+      ("b19200 Serialport", testSerialport CS19200),
+      ("b57600 Serialport", testSerialport CS57600),
+      ("b115200 Serialport",testSerialport CS115200),
+      ("b9600 Handle",      testHandle CS9600),
+      ("test delay",        testDelay)
+      ]
+
+
+main :: IO ExitCode
+main = do
+  [control_port, test_port] <- getArgs
+  cnts <- withSerial control_port defaultSerialSettings (runTestTT . tests test_port)
+  if failures cnts == 0
+    then exitSuccess
+    else exitFailure
+