Show diff for golden test failures

haskell/Main.hs

@@ -43,7 +43,7 @@ main =
                             withResource (parseFile $ "../inputs/" <> t <> "/" <> pt) mempty \input ->
                                 testGroup pt $
                                     ( zip (map show [1 :: Int ..]) parts <&> \(n, pp) ->
-                                        goldenVsString n ("../outputs/" <> t <> "/" <> pt <> "/" <> n) $
+                                        goldenVsStringDiff n diffCommand ("../outputs/" <> t <> "/" <> pt <> "/" <> n) $
                                             TL.encodeUtf8 . pp <$> input
                                     )
                                         <> [testGroup "extra" $ extraTests isRealData ("../outputs/" <> t <> "/" <> pt <> "/extra/") input]

haskell/Pre.hs

@@ -41,6 +41,7 @@ module Pre (
     allUnorderedPairs,
     adjacentPairs,
     sortPair,
+    diffCommand,
 )
 where
 
@@ -122,3 +123,6 @@ adjacentPairs = \case
 
 sortPair :: (Ord a) => (a, a) -> (a, a)
 sortPair (a, b) = if a <= b then (a, b) else (b, a)
+
+diffCommand :: FilePath -> FilePath -> [String]
+diffCommand a b = ["diff", "--color=always", a, b]

haskell/Puzzles/Day4.hs

@@ -31,7 +31,7 @@ puzzle =
                 let frames = Seq.fromList . takeUntil noneAccessible . fmap snd . generateFrames . mkGrid <$> input
                     nFrames = if isRealData then 58 else 9
                  in ( [0 .. nFrames] <&> \n ->
-                        goldenVsString (show n) (path <> "frames/" <> show n) $
+                        goldenVsStringDiff (show n) diffCommand (path <> "frames/" <> show n) $
                             TL.encodeUtf8 . maybe "frame list too short!" drawGrid . Seq.lookup n <$> frames
                     )
                         <> [ testCase "end" do