find and correct single bit errors in 16-bit hamming codes

test/Hamming/Word16Spec.hs

@@ -21,6 +21,7 @@ License along with this program.  If not, see
 
 module Hamming.Word16Spec (spec) where
 
+import Data.Bits (shiftL, xor)
 import Data.Word (Word16)
 
 import Hamming
@@ -61,8 +62,21 @@ isValidSpec = describe "isValid" $ mapM_
   ]
 
 correctErrorsSpec :: Spec
-correctErrorsSpec = describe "correctErrors" $
-  return ()
+correctErrorsSpec = describe "correctErrors" $ mapM_
+  ( \(desc, code, expected) -> context desc $ let
+    actual = correctErrors code
+    in it ("should be " ++ show expected) $
+      actual `shouldBe` expected
+  ) $ ("valid", withChkBits, Just withChkBits) :
+  singleBitErrors
+
+singleBitErrors :: [(String, Word16, Maybe Word16)]
+singleBitErrors = map
+  ( \bit -> let
+    mask = 1 `shiftL` bit
+    code = withChkBits `xor` mask
+    in ("bad bit " ++ show bit, code, Just withChkBits)
+  ) [0..15]
 
 noChkBits :: Word16
 noChkBits = 0x34c0