Johannes Schindelin <Johannes.Schindelin@xxxxxx> 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 :<
