scrabble-score: Test entire alphabet (#479)

exercism/problem-specifications#509
exercism/problem-specifications#516

Author: petertseng

exercises/scrabble-score/test/Tests.hs

@@ -23,7 +23,7 @@ specs = describe "scrabble-score" $ do
       where
         assertion = scoreWord input `shouldBe` fromIntegral expected
 
--- Test cases adapted from `exercism/x-common/scrabble-score.json` on 2016-07-26.
+-- Test cases adapted from `exercism/x-common/scrabble-score.json` on 2017-01-31.
 
 data Case = Case { description :: String
                  , input       :: String
@@ -75,4 +75,8 @@ cases = [ Case { description = "lowercase letter"
                , input       = ""
                , expected    = 0
                }
+        , Case { description = "entire alphabet available"
+               , input       = "abcdefghijklmnopqrstuvwxyz"
+               , expected    = 87
+               }
         ]