quickCheckAll总是返回“真” [英] quickCheckAll always return "True"

问题描述

我尝试使用另一个回答使用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 
 putStrLnquickCheck
 quickCheck（prop_test :: [Char]  - > Bool）
 
 check2 = do 
 putStrLnquickCheckAll 
 $ quickCheckAll 
  

然后我将它载入winGHCI并调用 check 和 check2 。我得到

  quickCheck 
 ***失败！ （1测试后）：
例外：
 list.hs：（7,1） - （8,23）：函数last'
中的非穷举模式
  

我认为这是合理的。但是，我从 check2

中得到了这个结果

$ p $ quickCheckAll
True


我很困惑，因为无论我如何更改 last'函数，甚至是错误的， quickCheckAll 总是返回True。

我的代码出了什么问题？我该如何解决这个问题？

解决方案

从 Test.QuickCheck.All 文档：

要使用 quickCheckAll ，请在模块中添加一个定义到

  return [] 
 runTests = $ quickCheckAll 
  

然后执行 runTests 。

注意：GHC 7.8需要上述示例中的奇怪 return [] ;没有它， quickCheckAll 将无法找到任何属性。

$ 在您的检查前添加 return [] / code>使它适用于我。

I'm trying to use QuickCheck following another answer. I test like this:

{-# 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

Then I load it in winGHCI and call check and check2. I get

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

which I think it's reasonable. However, I get this from check2

quickCheckAll
True

I'm confused because no matter how I change the last' function, even wrong, quickCheckAll always return True.

What's wrong with my code? How can I fix this?

解决方案

From the Test.QuickCheck.All docs:

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.

Adding return [] before your check makes it work for me.

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