Re: [PATCH] CONTRIBUTE - writing tests for understanding internals

["Andreas Röhler" <andreas.roehler@online.de>]

  On 13.11.2015 08:33, Eli Zaretskii wrote:
>> Cc: emacs-devel@gnu.org
>> From: Przemysław Wojnowski<esperanto@cumego.com>
>> Date: Thu, 12 Nov 2015 22:42:43 +0100
>>
>> W dniu 12.11.2015 o 21:55, Eli Zaretskii pisze:
>>> In TDD, they teach you to write a test for a spec that isn't
>>> implemented yet.  The test fails, of course (which is a Good Thing:
>>> now you know that your test indeed will catch a non-compliant
>>> implementation), and then you implement the spec to see that it now
>>> succeeds.  If you work that way, tests _do_ drive the development.
>> What do you mean by "spec" here?
> Sorry for using jargon here.  By "spec" I meant the specification of
> the module, i.e. the APIs of its methods, and the set of requirements
> that define what should be the result(s) of invoking the various
> methods with the various possible combinations of arguments and given
> the relevant environmental conditions.
>
> A simple example of a "spec" for a single function is what you see
> here:
>
>    http://pubs.opengroup.org/onlinepubs/009695399/functions/stat.html
>
>> I've never seen nor used TDD (and I use it very often) with "spec".
>> What I've seen, though, was using TDD to implement User Stories (Use
>> Cases), which are descriptions of functionality, but far from formal
>> specifications - if this is what you mean.
> A spec in the terminology I used is the set of formal requirements
> produced by analyzing those use cases.
>
> For the purposes of this discussion, I think it's immaterial whether
> the "spec" is formal or not.  What's important is that you can
> unequivocally determine what the code should do, and write the tests
> which check that.
>
>> Anyway, TDD drives design (you implement only as much as is needed to
>> make the tests pass) and, by side effect, gives strong regression test
>> suite, which _enables_ refactoring.
> Indeed.
>
>

Agreed WRT mentioned side effect - and its importance.

Cheers,

Andreas