Re: [PATCH/RFC/GSOC] make git-pull a builtin

[Paul Tan <pyokagan@gmail.com>]

Hi,

On Sun, Mar 22, 2015 at 1:35 AM, Johannes Schindelin
<johannes.schindelin@gmx.de> wrote:
>> Maybe code coverage tools could help here so we only need to focus on
>> the code paths that are untested by the test suite. At the minimum,
>> all of the non-trivial code paths in both the shell script and the
>> converted builtin must be covered by tests. This should help to
>> eliminate most sources of breakages. Anything further than that would
>> require an experienced understanding of all the possible important
>> inputs to be tested, which I personally feel would make the project
>> quite tedious.
>>
>> I see git already has gcov support. For shell scripts, maybe kcov[1]
>> could be used. With some slight code changes, I managed to generate a
>> report for the git-pull tests[2] which should at least provide a good
>> starting point for how the tests can be improved.
>
> While it is often a tempting idea to make test suites as thorough as possible, there lies a true danger herein. True war story: in one of the projects I was involved in, the test suite grew to a size that one complete run lasted two weeks. Yes, that is fourteen days. Needless to say: this test suite was run rarely. How useful is a test suite that is run rarely? More useful than a non-existent one, to be sure, but it is still more of a burden than a boon.
>
> Now, on Windows the test suite takes almost three hours to run. This really, really slows down development.
>
> So while we are not yet at the "too large to be useful state", I would caution against trying to get there.
>
> Instead, I would really like to focus on the *usage*. Calling `git grep "git pull" t/` should give you an idea what usage of `git pull` is already tested. It should be pretty easy to come up with a list of *common* use cases, and if any of them are not covered, adding tests for them is simple and straight-forward, too.

The code coverage tools can help here as well. The kcov output clearly
shows which options of git-pull are currently not being tested. But
yes, I agree that the test suite shouldn't be relied too much on
compared to code inspection and review.

On another important topic, though, along with git-pull.sh, I'm
looking for another script to convert in parallel with git-pull.sh so
that there will be no blocks due to patch review. Generally, I think
rewriting scripts that are called frequently by users, or spawn a lot
of processes due to loops, would be most desirable because the runtime
gains would be much higher. A quick review of the scripts shows that
git-am.sh, git-rebase--interactive.sh and git-quiltimport.sh have
pretty heavy loops with lots of process spawning that grows with
input.

I'm currently leaning with git-am because not only is it a frequently
used command, git-rebase--am.sh (for non-interactive rebase) calls it
as well. In fact, quick tests show that it takes up 98% of
git-rebase's execution time on Windows, so if git-am's performance
improves it would be a huge win on many fronts. git-am's code also
seems to be manageable for a 3-month project.

Anyway, I would like to know if you (or anyone else) have any scripts in mind.

(I also think that just 2 scripts would be enough to fill the 3
months, but that might be me just being too conservative)

Regards,
Paul