From: Eric Wong <e@80x24.org>
To: Johannes Schindelin <Johannes.Schindelin@gmx.de>
Cc: Emily Shaffer <emilyshaffer@google.com>,
Jeff King <peff@peff.net>,
Jonathan Tan <jonathantanmy@google.com>,
git@vger.kernel.org
Subject: Re: Git in Outreachy December 2019?
Date: Tue, 24 Sep 2019 00:55:29 +0000 [thread overview]
Message-ID: <20190924005529.GA8354@dcvr> (raw)
In-Reply-To: <nycvar.QRO.7.76.6.1909171158090.15067@tvgsbejvaqbjf.bet>
Johannes Schindelin <Johannes.Schindelin@gmx.de> wrote:
> On Mon, 16 Sep 2019, Emily Shaffer wrote:
> > - try and make progress towards running many tests from a single test
> > file in parallel - maybe this is too big, I'm not sure if we know how
> > many of our tests are order-dependent within a file for now...
>
> Another, potentially more rewarding, project would be to modernize our
> test suite framework, so that it is not based on Unix shell scripting,
> but on C instead.
I worry more C would reduce the amount of contributors (some of
the C rewrites already scared me off hacking years ago). I
figure more users are familiar with sh than C.
It would also increase the disparity between tests and use of
actual users from the command-line.
> The fact that it is based on Unix shell scripting not only costs a lot
> of speed, especially on Windows, it also limits us quite a bit, and I am
> talking about a lot more than just the awkwardness of having to think
> about options of BSD vs GNU variants of common command-line tools.
I agree that it costs a lot of time, and I'm even on Linux using
dash as /bin/sh + eatmydata (but ancient laptop)
> For example, many, many, if not all, test cases, spend the majority of
> their code on setting up specific scenarios. I don't know about you,
> but personally I have to dive into many of them when things fail (and I
> _dread_ the numbers 0021, 0025 and 3070, let me tell you) and I really
> have to say that most of that code is hard to follow and does not make
> it easy to form a mental model of what the code tries to accomplish.
>
> To address this, a while ago Thomas Rast started to use `fast-export`ed
> commit histories in test scripts (see e.g. `t/t3206/history.export`). I
> still find that this fails to make it easier for occasional readers to
> understand the ideas underlying the test cases.
>
> Another approach is to document heavily the ideas first, then use code
> to implement them. For example, t3430 starts with this:
>
> [...]
>
> Initial setup:
>
> -- B -- (first)
> / \
> A - C - D - E - H (master)
> \ \ /
> \ F - G (second)
> \
> Conflicting-G
>
> [...]
>
> test_commit A &&
> git checkout -b first &&
> test_commit B &&
> git checkout master &&
> test_commit C &&
> test_commit D &&
> git merge --no-commit B &&
> test_tick &&
> git commit -m E &&
> git tag -m E E &&
> git checkout -b second C &&
> test_commit F &&
> test_commit G &&
> git checkout master &&
> git merge --no-commit G &&
> test_tick &&
> git commit -m H &&
> git tag -m H H &&
> git checkout A &&
> test_commit conflicting-G G.t
>
> [...]
>
> While this is _somewhat_ better than having only the code, I am still
> unhappy about it: this wall of `test_commit` lines interspersed with
> other commands is very hard to follow.
Agreed. More on the readability part below...
As far as speeding that up, I think moving some parts
of test setup to Makefiles + fast-import/fast-export would give
us a nice balance of speed + maintainability:
1. initial setup is done using normal commands (or graph drawing tool)
2. the result of setup is "built" with fast-export
3. test uses fast-import
Makefile rules would prevent subsequent test runs from repeating
1. and 2.
> If we were to (slowly) convert our test suite framework to C, we could
> change that.
>
> One idea would be to allow recreating commit history from something that
> looks like the output of `git log`, or even `git log --graph --oneline`,
> much like `git mktree` (which really should have been a test helper
> instead of a Git command, but I digress) takes something that looks like
> the output of `git ls-tree` and creates a tree object from it.
I've been playing with Graph::Easy (Perl5 module) in other
projects, and I also think the setup could be more easily
expressed with a declarative language (e.g. GNU make)
> Another thing that would be much easier if we moved more and more parts
> of the test suite framework to C: we could implement more powerful
> assertions, a lot more easily. For example, the trace output of a failed
> `test_i18ngrep` (or `mingw_test_cmp`!!!) could be made a lot more
> focused on what is going wrong than on cluttering the terminal window
> with almost useless lines which are tedious to sift through.
I fail to see how language choice here matters. But then again,
I have plenty of experience writing bad code in ALL languages I
know :>
> Likewise, having a framework in C would make it a lot easier to improve
> debugging, e.g. by making test scripts "resumable" (guarded by an
> option, it could store a complete state, including a copy of the trash
> directory, before executing commands, which would allow "going back in
> time" and calling a failing command with a debugger, or with valgrind, or
> just seeing whether the command would still fail, i.e. whether the test
> case is flaky).
Resumability sounds like a perfect job for GNU make.
(that said, I don't know if you use make or something else to build gfw)
> In many ways, our current test suite seems to test Git's functionality
> as much as (core) contributors' abilities to implement test cases in
> Unix shell script, _correctly_, and maybe also contributors' patience.
> You could say that it tests for the wrong thing at least half of the
> time, by design.
Basic (not advanced) sh is already a prerequisite for using git.
Writing correct code and tests in ANY language is still a
challenge for me; but I'm least convinced a low-level language
such as C is the right language for writing integration tests in.
C is fine for unit tests, and maybe we can use more unit tests
and less integration tests.
> It might look like a somewhat less important project, but given that we
> exercise almost 150,000 test cases with every CI build, I think it does
> make sense to grind our axe for a while, so to say.
Something that would benefit both users and regular contributors
is the use and adoption of more batch and eval-friendly interfaces.
e.g. fast-import/export, cat-file --batch, for-each-ref --perl...
I haven't used hg since 2005, but I know "hg server" exists
nowadays to get rid of a lot of startup overhead in Mercurial,
and maybe git could steal that idea, too...
> Therefore, it might be a really good project to modernize our test
> suite. To take ideas from modern test frameworks such as Jest and try to
> bring them to C. Which means that new contributors would probably be
> better suited to work on this project than Git old-timers!
>
> And the really neat thing about this project is that it could be done
> incrementally.
I hope to find time to hack some more batch/eval-friendly stuff
that can make scripting git more performant; but no idea on my
availability :<
next prev parent reply other threads:[~2019-09-24 0:55 UTC|newest]
Thread overview: 63+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-08-27 5:17 Git in Outreachy December 2019? Jeff King
2019-08-31 7:58 ` Christian Couder
2019-08-31 19:44 ` Olga Telezhnaya
2019-09-04 19:41 ` Jeff King
2019-09-05 7:24 ` Christian Couder
2019-09-05 19:39 ` Emily Shaffer
2019-09-06 11:55 ` Carlo Arenas
2019-09-07 6:39 ` Jeff King
2019-09-07 10:13 ` Carlo Arenas
2019-09-07 6:36 ` Jeff King
2019-09-08 14:56 ` Pratyush Yadav
2019-09-09 17:00 ` Jeff King
2019-09-23 18:07 ` SZEDER Gábor
2019-09-26 9:47 ` SZEDER Gábor
2019-09-26 19:32 ` Johannes Schindelin
2019-09-26 21:54 ` SZEDER Gábor
2019-09-26 11:42 ` Johannes Schindelin
2019-09-13 20:03 ` Jonathan Tan
2019-09-13 20:51 ` Jeff King
2019-09-16 18:42 ` Emily Shaffer
2019-09-16 21:33 ` Eric Wong
2019-09-16 21:44 ` SZEDER Gábor
2019-09-16 23:13 ` Jonathan Nieder
2019-09-17 0:59 ` Jeff King
2019-09-17 11:23 ` Johannes Schindelin
2019-09-17 12:02 ` SZEDER Gábor
2019-09-23 12:47 ` Johannes Schindelin
2019-09-23 16:58 ` SZEDER Gábor
2019-09-26 11:04 ` Johannes Schindelin
2019-09-26 13:28 ` SZEDER Gábor
2019-09-26 19:39 ` Johannes Schindelin
2019-09-26 21:44 ` SZEDER Gábor
2019-09-27 22:18 ` Jeff King
2019-10-09 17:25 ` SZEDER Gábor
2019-10-11 6:34 ` Jeff King
2019-09-23 18:19 ` Jeff King
2019-09-24 14:30 ` Johannes Schindelin
2019-09-17 15:10 ` Christian Couder
2019-09-23 12:50 ` Johannes Schindelin
2019-09-23 19:30 ` Jeff King
2019-09-23 18:07 ` Jeff King
2019-09-24 14:25 ` Johannes Schindelin
2019-09-24 15:33 ` Jeff King
2019-09-28 3:56 ` Junio C Hamano
2019-09-24 0:55 ` Eric Wong [this message]
2019-09-26 12:45 ` Johannes Schindelin
2019-09-30 8:55 ` Eric Wong
2019-09-28 4:01 ` Junio C Hamano
2019-09-20 17:04 ` Jonathan Tan
2019-09-21 1:47 ` Emily Shaffer
2019-09-23 14:23 ` Christian Couder
2019-09-23 19:40 ` Jeff King
2019-09-23 22:29 ` Philip Oakley
2019-10-22 21:16 ` Emily Shaffer
2019-09-23 11:49 ` Christian Couder
2019-09-23 17:58 ` Jonathan Tan
2019-09-23 19:27 ` Jeff King
2019-09-23 20:48 ` Jonathan Tan
2019-09-23 19:15 ` Jeff King
2019-09-23 20:38 ` Jonathan Tan
2019-09-23 21:28 ` Jeff King
2019-09-24 17:07 ` Jonathan Tan
2019-09-26 7:09 ` Jeff King
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