简单的haskell单元测试 [英] Simple haskell unit testing

问题描述

我想通过 99个Haskell问题，我想专注于解决方案，但与测试。如果我将第一个问题的解决方案作为3行 .hs 文件，则可以使用

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

我可以添加的最小代码量是多少，以便我可以添加内联测试并使用 runhaskell ？

运行它们

解决方案

QuickCheck （其中basicaly生成测试输入为你）可能是测试纯功能的最好方法。如果有问题的函数有标准库的类比，那么你可以使用标准函数作为模型来测试你的函数：

  { - ＃LANGUAGE TemplateHaskell＃ - } 
 
 import Test.QuickCheck 
 import Test.QuickCheck.All 
 
 myLast :: [a]  - > a 
 myLast [x] = x 
 myLast（_：xs）= myLast xs 
 
  - 这里我们指定'myLast'应该返回完全相同的结果
  - 作为'最后'的任何给定的'xs'
 prop_myLast xs = myLast xs ==上一个xs 
 
 
返回[]  - 需要GHC 7.8 
  -  quickCheckAll为所有'prop_ *'属性生成测试用例
 main = $（quickCheckAll）
  

如果你运行它，你会得到：

  === prop_myLast on tmp3.hs：12 === 
 ***失败！例外：'tmp3.hs：（7,1） - （8,25）：函数myLast'中的非穷举模式（1测试后）：
 [] 
 False 
  

因为您的 myLast 不处理 [ ] case（它应该但应该抛出一个像'last'的错误）。
但是在这里，我们可以简单地调整我们的测试，但指定只应使用非空字符串（使用 ==> combinator）：

  prop_myLast xs = length xs> 0 ==> myLast xs == last xs 
  

这使得所有100个自动生成的测试用例都可以通过 myLast ：

  === prop_myLast on tmp3.hs：11 === 
 +++ OK，通过了100次测试。 
 True 
  

PS另一种指定 myLast 行为可能是：
$ b $ pre $ prop_myLast2 x xs = myLast（xs ++ [x]）== x


或者更好：



  prop_myLast3 x xs = x`notElem` xs ==> myLast（xs ++ [x]）== x 
  




I want to go through 99 Haskell Problems, and I want to concentrate on the solution but with testing. If I have the solution to the first problem as a 3 line .hs file,

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

What is the minimal amount of code I can add to this so that I can add tests inline and run them with runhaskell?

解决方案

QuickCheck (which basicaly generates test inputs for you) is probably the best way to test pure function. And if a function in question has an analog from the standard library you can just test your function using the standard one as a model:

{-# LANGUAGE TemplateHaskell #-}

import Test.QuickCheck
import Test.QuickCheck.All

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

-- here we specify that 'myLast' should return exactly the same result
-- as 'last' for any given 'xs'
prop_myLast xs = myLast xs == last xs


return [] -- need this for GHC 7.8
-- quickCheckAll generates test cases for all 'prop_*' properties
main = $(quickCheckAll)

If you run it you'll get:

=== prop_myLast on tmp3.hs:12 ===
*** Failed! Exception: 'tmp3.hs:(7,1)-(8,25): Non-exhaustive patterns in function myLast' (after 1 test):  
[]
False

because your myLast doesn't handle [] case (it should but should probably throw an error like 'last'). But here we can simply adjust our test but specifying that only non-empty strings should be used (using ==> combinator):

prop_myLast xs = length xs > 0 ==> myLast xs == last xs

Which makes all 100 auto-generated test cases to pass for myLast:

=== prop_myLast on tmp3.hs:11 ===
+++ OK, passed 100 tests.
True

PS Another way to specify myLast behavior may be:

prop_myLast2 x xs = myLast (xs++[x]) == x

Or better:

prop_myLast3 x xs = x `notElem` xs ==> myLast (xs++[x]) == x

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