largest-series-product: Rewrite tests to use hspec with fail-fast.

exercises/largest-series-product/package.yaml

@@ -9,11 +9,12 @@ library:
   dependencies:
   # - foo       # List here the packages you
   # - bar       # want to use in your solution.
+    - safe
 
 tests:
   test:
     main: Tests.hs
     source-dirs: test
     dependencies:
       - largest-series-product
-      - HUnit
+      - hspec

exercises/largest-series-product/src/Example.hs

@@ -1,15 +1,20 @@
 module Series (largestProduct) where
-import Data.Char (digitToInt)
-import Data.List (tails)
 
-digits :: Integral a => String -> [a]
-digits = map $ fromIntegral . digitToInt
+import Control.Monad    ((>=>))
+import Data.Char        (digitToInt, isDigit)
+import Data.List        (tails)
+import Data.Maybe       (mapMaybe)
+import Safe             (maximumMay)
+import Safe.Exact       (takeExactMay)
 
-slices :: Integral a => Int -> String -> [[a]]
-slices n = go . digits
-  where go xs = map (take n) $ take (length xs - pred n) (tails xs)
+-- base >= 4.8 re-exports `Data.Traversable.traverse`.
+import Data.Traversable -- This is only need for `traversable`.
+import Prelude          -- This trick avoids a warning if GHC >= 7.10.
 
-largestProduct :: Integral a => Int -> String -> Maybe a
-largestProduct n text = case map product (slices n text) of
-  []       -> Nothing
-  products -> Just $ maximum products
+largestProduct :: (Integral a, Num b, Ord b) => a -> String -> Maybe b
+largestProduct n = traverse charToNum >=> maximumMay . products
+  where
+    products = mapMaybe (fmap product . takeExactMay (fromIntegral n)) . tails
+    charToNum x
+        | isDigit x = Just . fromIntegral . digitToInt $ x
+        | otherwise = Nothing

exercises/largest-series-product/test/Tests.hs

@@ -1,41 +1,104 @@
-import Test.HUnit ((@=?), runTestTT, Test(..), Counts(..))
-import System.Exit (ExitCode(..), exitWith)
-import Series (largestProduct)
+{-# OPTIONS_GHC -fno-warn-type-defaults #-}
+
+import Test.Hspec        (Spec, describe, it, shouldBe)
+import Test.Hspec.Runner (configFastFail, defaultConfig, hspecWith)
 
-exitProperly :: IO Counts -> IO ()
-exitProperly m = do
-  counts <- m
-  exitWith $ if failures counts /= 0 || errors counts /= 0 then ExitFailure 1 else ExitSuccess
+import Series (largestProduct)
 
 main :: IO ()
-main = exitProperly $ runTestTT $ TestList
-  [ TestList seriesTests ]
-
--- Allow implementations that work with Integral to compile without warning
-int :: Int -> Maybe Int
-int = Just
-
-intNothing :: Maybe Int
-intNothing = Nothing
-
-seriesTests :: [Test]
-seriesTests = map TestCase
-  [ int 72 @=? largestProduct 2 "0123456789"
-  , int 2 @=? largestProduct 2 "12"
-  , int 9 @=? largestProduct 2 "19"
-  , int 48 @=? largestProduct 2 "576802143"
-  , int 504 @=? largestProduct 3 ['0'..'9']
-  , int 270 @=? largestProduct 3 "1027839564"
-  , int 15120 @=? largestProduct 5 ['0'..'9']
-  , int 23520 @=?
-    largestProduct 6 "73167176531330624919225119674426574742355349194934"
-  , int 28350 @=?
-    largestProduct 6 "52677741234314237566414902593461595376319419139427"
-  , int 1 @=? largestProduct 0 ""
-  , int 1 @=? largestProduct 0 "123"
-  , intNothing @=? largestProduct 1 ""
-  , intNothing @=? largestProduct 4 "123"
-    -- if all spans contain zero, result is zero.
-  , int 0 @=? largestProduct 3 "99099"
-  , int 0 @=? largestProduct 2 "00"
-  ]
+main = hspecWith defaultConfig {configFastFail = True} specs
+
+specs :: Spec
+specs = describe "largest-series-product" $
+
+    -- Test cases adapted from `exercism/x-common/largest-series-product.json`
+    -- on 2016-07-27.
+
+    describe "largestProduct" $ do
+
+      it "can find the largest product of 2 with numbers in order" $
+        largestProduct 2 "0123456789"
+        `shouldBe` Just 72
+
+      it "can find the largest product of 2" $
+        largestProduct 2 "576802143"
+        `shouldBe` Just 48
+
+      it "finds the largest product if span equals length" $
+        largestProduct 2 "29"
+        `shouldBe` Just 18
+
+      it "can find the largest product of 3 with numbers in order" $
+        largestProduct 3 "0123456789"
+        `shouldBe` Just 504
+
+      it "can find the largest product of 3" $
+        largestProduct 3 "1027839564"
+        `shouldBe` Just 270
+
+      it "can find the largest product of 5 with numbers in order" $
+        largestProduct 5 "0123456789"
+        `shouldBe` Just 15120
+
+      it "can get the largest product of a big number" $
+        largestProduct 6 "73167176531330624919225119674426574742355349194934"
+        `shouldBe` Just 23520
+
+      it "can get the largest product of a big number II" $
+        largestProduct 6 "52677741234314237566414902593461595376319419139427"
+        `shouldBe` Just 28350
+
+      it "can get the largest product of a big number (Project Euler)" $
+        largestProduct 13 "73167176531330624919225119674426574742355349194934\
+                          \96983520312774506326239578318016984801869478851843\
+                          \85861560789112949495459501737958331952853208805511\
+                          \12540698747158523863050715693290963295227443043557\
+                          \66896648950445244523161731856403098711121722383113\
+                          \62229893423380308135336276614282806444486645238749\
+                          \30358907296290491560440772390713810515859307960866\
+                          \70172427121883998797908792274921901699720888093776\
+                          \65727333001053367881220235421809751254540594752243\
+                          \52584907711670556013604839586446706324415722155397\
+                          \53697817977846174064955149290862569321978468622482\
+                          \83972241375657056057490261407972968652414535100474\
+                          \82166370484403199890008895243450658541227588666881\
+                          \16427171479924442928230863465674813919123162824586\
+                          \17866458359124566529476545682848912883142607690042\
+                          \24219022671055626321111109370544217506941658960408\
+                          \07198403850962455444362981230987879927244284909188\
+                          \84580156166097919133875499200524063689912560717606\
+                          \05886116467109405077541002256983155200055935729725\
+                          \71636269561882670428252483600823257530420752963450"
+        `shouldBe` Just 23514624000
+
+      it "reports zero if the only digits are zero" $
+        largestProduct 2 "0000"
+        `shouldBe` Just 0
+
+      it "reports zero if all spans include zero" $
+        largestProduct 3 "99099"
+        `shouldBe` Just 0
+
+      it "rejects span longer than string length" $
+        largestProduct 4 "123"
+        `shouldBe` Nothing
+
+      it "reports 1 for empty string and empty product (0 span)" $
+        largestProduct 0 ""
+        `shouldBe` Just 1
+
+      it "reports 1 for nonempty string and empty product (0 span)" $
+        largestProduct 0 "123"
+        `shouldBe` Just 1
+
+      it "rejects empty string and nonzero span" $
+        largestProduct 1 ""
+        `shouldBe` Nothing
+
+      it "rejects invalid character in digits" $
+        largestProduct 2 "1234a5"
+        `shouldBe` Nothing
+
+      it "rejects negative span" $
+        largestProduct (-1) "12345"
+        `shouldBe` Nothing