[QuickCheck] Test of type Property doesn't report counter example

[Nick Smallbone]

Hi Lennart,

Thanks for the bug report. This is a regression in 2.7 that appeared
when we changed Property from a type synonym to a newtype. I've pushed
a patch to fix it which should be on Hackage in a few days.

Nick

On Friday 25 April, 2014 at 11:47 pm, Lennart Kolmodin wrote:
> Hi,
> 
> I ran into an issue where a test that fails with an exception does not
> report the input given to that test.
> 
> As an example, see this simple test;
> 
> quickCheck $ \x -> if (x == 10) then error "oh noes" else property True
> 
> This test either succeeds;
> +++ OK, passed 100 tests.
> or fails;
> *** Failed! Exception: 'oh noes' (after 32 tests):
> 
> Notice the lack of the counter example!
> 
> Now if we change the test slightly, and make it Bool instead of Property;
> 
> quickCheck $ \x -> if (x == 10) then error "oh noes" else True
> 
> It either succeeds or fails with;
> *** Failed! Exception: 'oh noes' (after 11 tests):
> 10
> 
> Aha! The counter example is given!
> 
> If we don't throw an exception but rather just fail the test with False;
> 
> quickCheck $ \x -> if (x == 10) then False else True
> or
> quickCheck $ \x -> if (x == 10) then property False else property True
> 
> The both succeed or fail with counter examples.
> 
> It looks to me that tests of type Property which fails with an exception
> doesn't give a counter example. It look useful to me if it gave a counter
> example also in this case.
> 
> Regards,
> Lennart

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