Question

考虑Haskell中的以下QuickCheck程序

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

prop_trivial :: Bool
prop_trivial = 42 == (6 * 7)

-- Wacky boilerplate to make all tests run.
return []
runTests = $quickCheckAll
main = do
  runTests

这适用于ghc版本7.8.3和QuickCheck 2.7.6。问题是它重复测试100次。我四处寻找缓解措施，并在the QuickCheck docs here中找到exhaustive。 Groovy的！我将prop_trivial更改为以下内容：

prop_trivial = exhaustive $ property $ 42 == (6 * 7)

进行类型检查和编译，但失败了：

=== prop_trivial from /blahblahblah/FooTest.hs:6 ===
*** Failed! Falsifiable (after 1 test): 
False

我对如何理解和调试此结果感到有点困惑;文档对我来说太薄了，无法弄清楚发生了什么。

Answer 1

您可能会喜欢smallcheck。它不像QuickCheck那样发达，但对于详尽的测试非常好。在QuickCheck生成随机输入的地方，smallcheck系统地生成其输入，在所有输入上运行属性，直到给定（由您）大小。对于人口数量有限的类型，这使得设置详尽的测试变得非常简单，并且因为我们不会尝试生成随机的东西，所以它也很容易避免重复测试。这是一个简单的例子：

Test.SmallCheck> smallCheck 10 (6*7 == 42)
Completed 1 tests without failure.

10是用于选择何时停止生成输入的最大深度;由于没有输入，因此在此示例中忽略了它。有关使用大小的示例，请考虑：

Test.SmallCheck> smallCheck 10 (\x -> x <= (10 :: Integer))
Completed 21 tests without failure.
Test.SmallCheck> smallCheck 20 (\x -> x <= (10 :: Integer))
Failed test no. 22.
there exists 11 such that
  condition is false

Answer 2

您似乎可以使用once修改属性以仅运行一次。

一些示例代码：

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

prop_trivial :: Int -> Bool
prop_trivial x = x == x
prop_trivial2 = once prop_trivial
prop_true = True
prop_true2 = once True

-- Wacky boilerplate to make all tests run.
return []
runTests = $quickCheckAll
main = do
  putStrLn $ "exhaustive prop_trivial  = " ++ show (exhaustive prop_trivial)
  putStrLn $ "exhaustive prop_trivial2 = " ++ show (exhaustive prop_trivial2)
  putStrLn $ "exhaustive prop_true     = " ++ show (exhaustive prop_true)
  putStrLn $ "exhaustive prop_true2    = " ++ show (exhaustive prop_true2)
  runTests

输出：

exhaustive prop_trivial  = False
exhaustive prop_trivial2 = False
exhaustive prop_true     = True
exhaustive prop_true2    = False
=== prop_trivial from qc2.hs:5 ===
+++ OK, passed 100 tests.

=== prop_trivial2 from qc2.hs:7 ===
+++ OK, passed 1 tests.

=== prop_true from qc2.hs:8 ===
+++ OK, passed 100 tests.

=== prop_true2 from qc2.hs:9 ===
+++ OK, passed 1 tests.

exhaustive prop 只有在知道 prop 的测试是详尽无遗的情况下才会返回True - 请注意exhaustive True和{{1}之间的区别}。

Answer 3

source非常简单。 exhaustive的默认定义用于Property实例，默认值为exhaustive _ = False。我想你可能想要exhaustive $ 42 == (6 * 7)

Haskell QuickCheck中的穷举属性？

3 个答案: