unit-testing - quickCheckAll 总是返回 "True"

Question

我正在尝试使用 another answer 之后的 QuickCheck .
我这样测试:

{-# LANGUAGE TemplateHaskell #-}
import Test.QuickCheck
import Test.QuickCheck.All


last' :: [a] -> a
last' [x] = x
last' (_:xs) = last' xs

prop_test x = last' x == last x

check = do
        putStrLn "quickCheck"
        quickCheck (prop_test :: [Char]-> Bool)

check2 = do
        putStrLn "quickCheckAll"
        $quickCheckAll

然后我将其加载到 winGHCI 并调用 check和 check2 .我明白了

quickCheck
*** Failed! (after 1 test): 
Exception:
  list.hs:(7,1)-(8,23): Non-exhaustive patterns in function last'
""

我认为这是合理的。但是，我从 check2 得到这个

quickCheckAll
True

我很困惑，因为无论我如何更改 last'函数，甚至错误， quickCheckAll总是返回 True。
我的代码有什么问题？我怎样才能解决这个问题？

Answer 1

来自 Test.QuickCheck.All 文档:

To use quickCheckAll, add a definition to your module along the lines of

return []
runTests = $quickCheckAll

and then execute runTests.

Note: the bizarre return [] in the example above is needed on GHC 7.8; without it, quickCheckAll will not be able to find any of the properties.

添加 return []在您的 check 之前让它对我有用。