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

[Lennart Kolmodin]

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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