FizzBuzzWithTests.hs

import Test.QuickCheck          

fizzBuzzinator a 
  | (mod a 15) == 0 = "fizzbuzz"
  | (mod a 3)  == 0 = "fizz"
  | (mod a 5)  == 0 = "buzz"
  | otherwise       = show a

fizzBuzz xs = unlines (map fizzBuzzinator xs)
    
main = do putStrLn (fizzBuzz [1..100])
          
-- Test Cases
testNumbers = forAll (choose (1,100)::Gen Int)

pred_nonDiv  x = ((mod x 3)  > 0 && (mod x 5)  > 0)
pred_div3    x = ((mod x 3) == 0 && (mod x 5)  > 0)
pred_div5    x = ((mod x 3)  > 0 && (mod x 5) == 0)
pred_divBoth x = ((mod x 3) == 0 && (mod x 5) == 0)

prop_num      x = (pred_nonDiv  x) ==> (fizzBuzzinator x) == (show x)
prop_fizz     x = (pred_div3    x) ==> (fizzBuzzinator x) == "fizz"
prop_buzz     x = (pred_div5    x) ==> (fizzBuzzinator x) == "buzz"
prop_fizzbuzz x = (pred_divBoth x) ==> (fizzBuzzinator x) == "fizzbuzz"

tests = do
  quickCheck (testNumbers $ prop_num)
  quickCheck (testNumbers $ prop_fizz)
  quickCheck (testNumbers $ prop_buzz) 
  quickCheck (testNumbers $ prop_fizzbuzz)