[QuickCheck] Unxpected compositional behaviour

Erik de Castro Lopo mle+hs at mega-nerd.com
Wed Jan 29 06:28:07 GMT 2014


Hi all,

This issue came up with respect to Hspec which uses QuickCheck as a
library:

     https://github.com/hspec/hspec/issues/149

but it seems to really be a QuickCheck issue which can be easily
demonstrated like this:

    ghci> import Test.QuickCheck
    ghci> let prop_foo = 1 == 2
    ghci> let prop_bar = 1 == 1
    ghci> quickCheck (property prop_foo >> property prop_bar)
    +++ OK, passed 100 tests.

The first of those properties should fail, but doesn't. I think, that
without knowing the current behaviour, most people asked to guess what
the behaviour *should* be would say that the first property should 
cause the failure of the whole test.

Do other people have the same view? Can this be easily fixed?

Cheers,
Erik
-- 
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Erik de Castro Lopo
http://www.mega-nerd.com/



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