I will answer myself, because it is possible that someone will need this answer. Reason of the problem was with one "test operator" only: `==>` - it's something like imlication but has one difference. I implemented own (standard) implication as: (-->) :: Bool -> Bool -> Bool True --> True = True True --> False = False False --> True = True False --> False = True infixr 0 --> and use it instead of `==>`. And with this operator (used in QuickCheck properties testing) I get output of case's values which leads to fail in my tests. So, test looks like: ... describe "Some func test" $ do prop "negative input becomes positive" $ do \n -> n < 0 --> someFunc n >= 0 ... To see all QuickCheck generated values, I can use alternative (verbose) `property` and `prop` funcs: verbproperty :: Testable prop => prop -> Expectation verbproperty p = verboseCheckResult p >>= (`shouldBe` True) . isSuccess verbprop :: (HasCallStack, Testable prop) => String -> prop -> Spec verbprop s = it s . vproperty All is for HSpec tests (with QuickCheck properties)... === Best regards, Paul

Hello, Dear List!

I have tests: I'm using HSpec (and QuickCheck too). And I have tests like this:

describe "Something" $ do it "something is correct" $ do ...blah-blah... it "any string is correct" $ property $ \s -> all (=='*') (Something s) -- it's for example only!!!

so something like unit-test and property checks in one SomethingSpec.hs.

I'm running them with this Makefile:

.PHONY: test fast-test

fast-test: stack exec runhaskell -- -isrc -itest test/Spec.hs

test: stack test

and in Spec.hs I have:

{-# OPTIONS_GHC -F -pgmF hspec-discover #-}

That's all. So, when I find failed test, I get a trace like this:

... Failures:

test/SomethingSpec.hs:172: 1) BlahBlah.superFunc any string is correct: result Gave up after 48 tests ...etc...

So, my question is: when QuichCheck runs my property test, it passes argument to property's lambda. And on 48th test attempt with some concreate argument value my check fails. How can I get detailed output from such test environment, to see what concreate arguments lead to failure? To see something (or similar/or more detailed even):

Failed with arguments: s = ""

Is it possible (I run them with stack and with runhaskell too) ?

=== Best regards, Paul