Cover our utility functons with unit tests

test/HCatSpec.hs

@@ -2,9 +2,11 @@
 
 module HCatSpec (spec) where
 
-import HCat.Internal (parseArgs)
+import HCat.Internal (chunksOf, parseArgs)
 
 import Test.Hspec
+import Test.Hspec.QuickCheck (prop)
+import Test.QuickCheck (Positive (getPositive))
 
 spec :: Spec
 spec = do
@@ -13,3 +15,13 @@ spec = do
       parseArgs ["foo"] `shouldBe` Right "foo"
       parseArgs [] `shouldBe` Left "No filename given!"
       parseArgs ["foo", "bar"] `shouldBe` Left "Only a single file is supported"
+  describe "chunksOf" $ do
+    prop "each chunk contains at most N items" $ \n xs ->
+      let chunkLengths = length <$> chunksOf n (xs :: [Int])
+       in case chunkLengths of
+            [] -> pure ()
+            ns -> maximum ns `shouldSatisfy` (<= n)
+
+    prop "the sum of all lengths is equal to the length of the input" $ \n xs ->
+      let chunkLengths = length <$> chunksOf (getPositive n) (xs :: [Int])
+       in sum chunkLengths `shouldBe` length xs