Re: GSoC 2019: Git's application submitted

From: Johannes Schindelin <Johannes.Schindelin@gmx.de>
To: Jeff King <peff@peff.net>
Cc: "Duy Nguyen" <pclouds@gmail.com>,
	"Christian Couder" <christian.couder@gmail.com>,
	git <git@vger.kernel.org>, "Stefan Beller" <sbeller@google.com>,
	"SZEDER Gábor" <szeder.dev@gmail.com>,
	"Thomas Gummerer" <t.gummerer@gmail.com>,
	"Оля Тележная" <olyatelezhnaya@gmail.com>,
	"Matthieu Moy" <Matthieu.Moy@gmail.com>
Subject: Re: GSoC 2019: Git's application submitted
Date: Wed, 6 Mar 2019 15:16:33 +0100 (STD)	[thread overview]
Message-ID: <nycvar.QRO.7.76.6.1903061515140.41@tvgsbejvaqbjf.bet> (raw)
In-Reply-To: <20190306044955.GC6664@sigill.intra.peff.net>

Hi Peff,

On Tue, 5 Mar 2019, Jeff King wrote:

> On Tue, Mar 05, 2019 at 07:04:59PM +0700, Duy Nguyen wrote:
> 
> > On Mon, Feb 4, 2019 at 4:17 PM Christian Couder
> > <christian.couder@gmail.com> wrote:
> > >
> > > Hi everyone,
> > >
> > > There are now ideas, micro-projects and organization application pages
> > > for GSoC 2019 on https://git.github.io/
> > >
> > > It would be nice to have a few more project ideas.
> > 
> > Not sure if it's too late now. Anyway this could be something fun to
> > do: support C-based tests in our test suite.
> > 
> > A while back I noticed some test running very long because it was
> > trying a lot of input combination. The actual logic is not much, but
> > because of the increasing number of test cases, overhead goes off the
> > roof. The last part is probably not true, but Windows port I think is
> > hit much harder than what I experience, and I think Dscho did complain
> > about it.
> > 
> > So what this project does is somehow allow people to write test cases
> > in C instead of shell. Imagine replacing t3070-wildmatch.sh with a
> > binary program t3070-wildmatch that behaves the same way. This test
> > framework needs to support the same basic feature set as test-lib.sh:
> > TAP output, test results summary, maybe -i and --valgrind... To
> > demonstrate that the test framework works, one of these long test
> > files should be rewritten in C. I'm sure there's one that is simple to
> > rewrite.
> > 
> > I'm pretty sure I had some fun with this idea and made some prototype
> > but I couldn't find it. If I do, I'll post the link here.
> 
> In my experience, it's nicer to have a tool written in C that can be
> driven by arbitrary input. That makes it easy to write new test cases,
> because you just have to write in some easy domain-specific format
> instead of embedding the test data in C code.
> 
> And many of our tests do work like that (in fact, many of the Git
> plumbing tools function as that). E.g., test-date gives you direct
> access to the low-level routines, and we feed it a variety of dates.
> 
> That doesn't help with the cost of invoking that tool over and over,
> though, once per test case. I wonder if we could have some kind of
> hybrid. I.e., where t3070 is still a shell script, but it primarily
> consists of running one big binary, like:
> 
>   test-wildmatch <<-\EOF
>   case 1
>   case 2
>   ...etc
>   EOF
> 
> but with one added twist: test-wildmatch would actually generate TAP
> output for each test, rather than just returning 0/1 for each success or
> failure, and being embedded in a test_expect_success.
> 
> It seems like that would even be pretty easy to do, with the exception
> of the numbering. It would be nice if we could intermingle this kind of
> "chunk of C tests" with normal tests, but we'd have to figure out how
> many tests it ran and increment our shell-script's counter
> appropriately.

Oooooh, that sounds like a very nice idea! Eventually, we might even be
able to specify our test cases in our own, extensible language, where we
do not have to pay attention to &&-chains, or portability, because our
test runner does all that for us, under the hood, as it should be.

Dreaming of that future,
Dscho