Quickcheck，使用一个函数来定义任意实例，该函数的结果取决于它的参数 [英] Quickcheck, defining Arbitrary instances using a function whose result depends on its arguments

问题描述

我有一个函数 arbExample 来产生一个随机的示例数据类型，这个数据类型取决于许多函数。

我试图通过做 quickCheck prop_example 来做一些属性测试，问题是我不知道如何使用 arbExample 为示例定义一个任意实例。

我喜欢在指定 Gens quickCheck prop_example $ c>数据结构 arbExample 使用。

  data示例=示例
 {myInt :: Int 
，myList :: [String] 
}派生（显示）
 
数据Gens = Gens 
 {gen1 :: Gen Int 
，gen2 :: Gen String} 
 
 arbExample :: Gens  - > Gen示例
 arbExample gens = do 
i <-gen1 gens 
 xs < -  vectorOf i（gen2 gens）
 return示例{myInt = i，myList = xs} 
 
 prop_example ::示例 - >属性
 prop_example示例= do 
 let len = length（myList示例）
 monadicIO $ do 
  - 运行程序的结果
成功<  - 运行$（ \e  - > return False）示例
 
的成功案例True  - > return（）
 False  - >失败失败
 
实例任意示例，其中
任意= arbExample _ { -  ??? - } 
  

解决方案

使用 forAll combinator具有签名：



  forAll ::（Show a，Testable prop）=> Gen a  - > （a  - > prop） - >物业
  

一个简单的例子：



  import Test.QuickCheck 
 
 genA :: Gen Int 
 genA =选择（-100,100）
 
 genB :: Gen Int 
 genB =选择（1,100）
 
 prop_example :: Int  - > Bool 
 prop_example n = n> 0 
 
 testA = quickCheck $ forAll genA prop_example 
 testB = quickCheck $ forAll genB prop_example 
  

testA 会失败，但 testB 会成功。

I have a function arbExample to generate a random Example data type which depends on a numbers of functions.

I am trying to do some property testing by doing quickCheck prop_example, the problem is I don't know how to define an Arbitrary instance for Example which uses arbExample.

I like to be able run quickCheck prop_example while specifying the Gens data structure which arbExample uses.

data Example = Example
    { myInt  :: Int 
    , myList :: [String]
    } deriving (Show)

data Gens =  Gens
    { gen1 :: Gen Int
    , gen2 :: Gen String }

arbExample :: Gens -> Gen Example
arbExample gens = do 
    i  <- gen1 gens 
    xs <- vectorOf i (gen2 gens)
    return Example{myInt=i, myList=xs}

prop_example :: Example -> Property
prop_example example =  do
    let len = length (myList example) 
    monadicIO $ do 
        -- result of running some program
        successful <- run $ (\e -> return False) example  
        case successful of
            True  -> return ()
            False -> fail "failure "

instance Arbitrary Example where
    arbitrary =  arbExample _ {- ??? -}

解决方案

Use the forAll combinator which has the signature:

forAll :: (Show a, Testable prop) => Gen a -> (a -> prop) -> Property

A quick example:

import Test.QuickCheck

genA :: Gen Int
genA = choose (-100,100)

genB :: Gen Int
genB = choose (1,100)

prop_example :: Int -> Bool
prop_example n = n > 0

testA = quickCheck $ forAll genA prop_example
testB = quickCheck $ forAll genB prop_example

testA will fail but testB will succeed.

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