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Programming with correctness guarantees
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Date: 2007-02-01 (20:36)
From: Robert Fischer <robert@f...>
Subject: Re: [Caml-list] Programming with correctness guarantees
What, exactly, is the difference between a unit test and formal
verification of an application?  I've long been under the opinion that
Design-by-Contract is just a way to write unit tests quickly -- after all,
you write something that looks kinda like code, attach it to something we
arbitrarily define as a "unit", run some framework on that, and the
framework tells you if something violates those rules.  This sounds like
unit testing to me.

Now, I could be wrong, and there could be something obvious I'm missing,
and I'd like to know if there is -- but it just doesn't seem like there's
anything like a clear line between unit tests and program verification.

Given that there isn't, it seems like people writing verified code aren't
really skipping the unit testing phase at all: they're just doing unit
testing in a funny way.

~~ Robert Fischer.
Fischer Venture Management Corporation

On Thu, February 1, 2007 2:12 pm, Jean-Christophe Filliatre wrote:
> Joshua D. Guttman writes:
>  > oleg@pobox.com writes:
>  >
>  > >   I remember reading somewhere that after a division of
>  > >   Siemens applied this technique to a high assurance
>  > >   project, they noted an exhilarating feeling of being
>  > >   able to program without unit tests. The code was correct
>  > >   by construction.
>  >
>  > This seems really frightening.
> There's a joke around in the formal methods community: ``would you
> prefer to get on a plane whose software has been proved correct or
> has been tested?''
> More seriously, I heard a similar remark from a French company which
> formally verified the embedded code of an automatic subway line (using
> the B method). They explained that, after the verification had been
> completed, the unit phase was not suppressed, but greatly reduced.
> --
> Jean-Christophe
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