CODEWITHSUNDEEP
haskellquickcheck
Tarick Welling
Tarick Welling

Reputation: 3265

How do I change the amount of tests for a custom generator?

So I have a property p :: Int -> Bool. I need to test it with a custom generator g :: Gen Int. This works and I can run

quickCheckResult $ forAll g p

I however want to have it run more than 100 tests. The documentation says use withMaxSuccess. This works for

quickCheck (withMaxSuccess 1000 p)

but not for

quickCheckResult $ forAll g (withMaxSuccess 1000 p)

because it results in a:

<interactive>:38:23: error:
    • Couldn't match expected type ‘Int -> prop0’
                  with actual type ‘Property’
    • Possible cause: ‘withMaxSuccess’ is applied to too many arguments
      In the second argument of ‘forAll’, namely
        ‘(withMaxSuccess 10000 p)’
      In the expression:
        forAll g (withMaxSuccess 10000 p)
      In an equation for ‘it’:
          it = forAll g (withMaxSuccess 10000 p)

It seems that withMaxSuccess takes the Int->Bool and makes it a Property

How can I run forAll for a arbitrary amount?

Upvotes: 1

Views: 117

Answers (1)

Mark Seemann
Mark Seemann

Reputation: 233327

You just need to compose the expressions slightly differently:

quickCheckResult $ withMaxSuccess 1000 $ forAll g p

or, if you prefer brackets:

quickCheckResult ((withMaxSuccess 1000) (forAll g p))

Looking at the types should explain why that works:

Prelude Test.QuickCheck> :t forAll g p
forAll g p :: Property

Prelude Test.QuickCheck> :t withMaxSuccess 1000
withMaxSuccess 1000 :: Testable prop => prop -> Property

Prelude Test.QuickCheck> :t (withMaxSuccess 1000) (forAll g p)
(withMaxSuccess 1000) (forAll g p) :: Property

Since Property is a Testable instance, the types line up.

Upvotes: 1

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