Cover our utility functons with unit tests

src/HCat/Internal.hs

@@ -1,8 +1,30 @@
 -- | Internal module in order to facilitate testability.
 module HCat.Internal where
 
+-- | @parseArgs@ takes a list of strings and returns a single FilePath if there was exactly one element.
+--
+-- >>> parseArgs ["foo"]
+-- Right "foo"
 parseArgs :: [String] -> Either String FilePath
 parseArgs args = case args of
     [] -> Left "No filename given!"
     [arg] -> Right arg
     _ -> Left "Only a single file is supported"
+
+-- | @chunksOf n@ splits a list into chunks of at most @n@ items.
+--
+-- >>> chunksOf 3 "abcdefgh"
+-- ["abc","def","gh"]
+--
+-- >>> chunksOf 0 "abcdefgh"
+-- []
+--
+-- >>> chunksOf (-1) "abcdefgh"
+-- []
+chunksOf :: Int -> [a] -> [[a]]
+chunksOf _ [] = []
+chunksOf n xs@(_ : _)
+    | n <= 0 = []
+    | otherwise =
+        let (chunk, rest) = splitAt n xs
+         in chunk : chunksOf n rest