基于属性的异常测试

Question

I am writing an introduction to Haskell for my local functional programming group. As a base I am using the Tasty-testing framework and I want to test the indexing function (!!) .

MinimalExample.hs

module MinimalExample where

myIndex :: Int -> [a] -> a                                               
myIndex _ [] = error "index too large"                                   
myIndex 0 (x:_) = x                                                      
myIndex n (_:xs) = myIndex (n-1) xs                                      

MinimalTests.hs

module MinimalTests where

import Test.Tasty
import Test.Tasty.SmallCheck as SC
import Test.SmallCheck.Series

import MinimalExample

main :: IO ()
main = defaultMain tests

tests :: TestTree
tests = testGroup "Tests" [scProps]

scProps ::  TestTree
scProps = testGroup "(checked by SmallCheck)"
  [ SC.testProperty "(!!) == myIndex" $ \lst n ->
      lst !! n == myIndex (n::Int) (lst::[Int])
  ]

The tests should not fail on "too large indices" as the Errors/Exceptions are the same.

The tests should fail with negative input - which could be resolved by adding NonNegative as a constraint on the input, or adding the respective clause in the myIndex -function.

• Can I test for exceptions in property based tests?
• Or do I have to use (H)Unit-tests like in How do I test for an error in Haskell? or Haskell exceptions and unit testing , in this case how do I choose the Index in the range of 0 to length of the generated testing list.

Answer 1

您可以使用spoon包，或者编写类似的函数，如果您想测试异常是否相同，将返回异常。