No output on Failed predicate

[Nimor111]

Hello,

This is a great package and i'd like to use it, but I have an issue that's making it basically impossible to use :/

I've setup this test:

propertySpec :: IO Connection -> Spec
propertySpec conn = describe "follows best practices" $ do
    it "doesn't return 500" $ do
        withServantServer api sserver $ \url ->
            serverSatisfies api url stdArgs (not500 <%> mempty)
    where
        sserver = do
            c <- conn
            pure $ server c

And i'm calling it from hspec like this:

  hspec $ propertySpec $ do
    pure conn

And the output i'm receiving on a failed response is:

Failures:

  src/Servant/QuickCheck/Internal/QuickCheck.hs:146:11:
  1) follows best practices doesn't return 500
       Failed:
       Nothing

  To rerun use: --match "/follows best practices/doesn't return 500/"

I've looked at the code and can't really make out why and how it's printing Nothing there, but trying with another property ( for example getsHaveCacheControlHeader ) it outputs the request and response as it should ( with the Show instance for PredicateFailure ).

I'm using version 0.0.8.0 of the package, the stack build tool, on NixOS. Happens on other Linux distros as well, without nix.

[worm2fed]

same problem with servant-quickcheck-0.0.10.0!

But sometimes there are Nothing and sometimes if I run test again I receive proper output.. so strange

[mgajda]

@worm2fed @Nimor111 Can you please confirm that #81 fixes the issue?

[worm2fed]

@mgajda I've tried to compile your branch.

so I have an error

src/Servant/QuickCheck/Internal/Equality.hs:26:32: error:
    • Could not deduce (Eq (Response b)) arising from a use of ‘==’
      from the context: Eq b
        bound by the type signature for:
                   allEquality :: forall b. Eq b => ResponseEquality b
        at src/Servant/QuickCheck/Internal/Equality.hs:25:1-41
    • In the first argument of ‘ResponseEquality’, namely ‘(==)’
      In the expression: ResponseEquality (==)
      In an equation for ‘allEquality’:
          allEquality = ResponseEquality (==)
   |
26 | allEquality = ResponseEquality (==)
   |     

Your branch depends on 0.0.9.1 version (https://github.com/mgajda/servant-quickcheck/blob/ede14d6414950ea482f65a9edf2408740e5dc187/servant-quickcheck.cabal#L2) and latest one is 0.0.10.0 (https://github.com/haskell-servant/servant-quickcheck/tree/v0.0.10.0) I guess this is the problem