Ævar Arnfjörð Bjarmason <avarab@xxxxxxxxx> writes: > On Thu, Feb 17 2022, Glen Choo wrote: > >> Ævar Arnfjörð Bjarmason <avarab@xxxxxxxxx> writes: >> >>> On Wed, Feb 16 2022, Glen Choo wrote: >>> >>>> Ævar Arnfjörð Bjarmason <avarab@xxxxxxxxx> writes: >>>> >>>>> On Wed, Feb 16 2022, Glen Choo wrote: >>>>> >>>>>> In a previous commit, we replaced test_cmp invocations with >>>>>> verify_fetch_result(). Finish the process of removing test_cmp by using >>>>>> grep in verify_fetch_result() instead. >>>>>> >>>>>> This makes the tests less sensitive to changes because, instead of >>>>>> checking the whole stderr, we only grep for the lines of the form >>>>>> >>>>>> * "<old-head>..<new-head>\s+branch\s+-> origin/branch" >>>>>> * "Fetching submodule <submodule-path>" (if fetching a submodule) >>>>>> >>>>>> when we expect the repo to have fetched. If we expect the repo to not >>>>>> have fetched, grep to make sure the lines are absent. Also, simplify the >>>>>> assertions by using grep patterns that match only the relevant pieces of >>>>>> information, e.g. <old-head> is irrelevant because we only want to know >>>>>> if the fetch was performed, so we don't need to know where the branch >>>>>> was before the fetch. >>>>> >>>>> I tried ejecting 1/9 and 2/9 out of this series locally, and it passes >>>>> all tests until the new tests you add in 7/9. >>>>> >>>>> As ugly as some of the pre-image is, I wonder if dropping these first >>>>> two and biting the bullet and just continuing with the test_cmp is >>>>> better. >>>>> >>>>> The test_cmp is going to catch issues that even the cleverest grep >>>>> combinations won't, e.g. in the submodule-in-C series I discovered a bug >>>>> where all of our testing & the existing series hadn't spotted that we >>>>> were dropping a \n at the end in one of the messages. >>>> >>>> I think there are two schools of thought on how to test informational >>>> messages: >>>> >>>> - assert an exact match on the exact output that we generate >>>> - assert that the output contains the pieces of information we care >>>> about >>>> >>>> These two approaches are virtually opposites on two axes - the former >>>> will catch unintentional changes (like you've noted)[...] >>> >>> Yes, and to be fair I'm thoroughly in the "assert an exact match" camp, >>> i.e. "let's just use test_cmp", and not everyone would agree with that. >>> >>> I mean, I don't think we should test_cmp every single instance of a >>> command, but for things that are *the tests* concerning themselves with >>> what the output should be, yes we should do that. >> >> That's a good point I hadn't considered, which is that if we want any >> hope of catching unintentional changes in our test suite, we'd want >> _some_ test to check the output. For "git fetch --recurse-submodules", >> it makes the most sense for that test to live in this file. >> >> By eliminating all instances of test_cmp in this file in particular, we >> lose assurances that we don't introduce accidental changes. It makes >> sense to at least have some tests explicitly for output. >> >>> >>>> [...] and the latter saves on maintenance effort and tends to be less noisy in tests. >>> >>> I also don't think you're right about the other approach "sav[ing] on >>> [future] maintenance effort" in this case. >>> >>> If I was needing to adjust some of this output I'd spend way longer on >>> trying to carefully reason that some series of "grep" invocations were >>> really doing the right thing, and probably end up doing the equivalent >>> of a "test_cmp" for myself out of general paranoia, whereas adjusting >>> the output. >> >> That's fair. I've optimized the tests for readability by putting >> complicated logic in the test helper. But any diligent test reader would >> need to read the test helper to convince themselves of its correctness. >> In this case, I agree that the helper is too complex. >> >>>> Personally, I'm a bit torn between both approaches in general because I >>>> want tests to be maintainable (testing the exact output is a bit of an >>>> antipattern at Google), but I'm not very comfortable with the fact that >>>> unintended changes can sneak through. >>> >>> Yes, anyway whatever one thinks in general what I meant to point out >>> here with "biting the bullet" is that whatever one thinks in general >>> about the right approch for new tests, this series in particular seems >>> to be creating more work for itself than it needs by refactoring the >>> test_cmp in existing tests just to add a few new ones. >>> >>> I.e. even if you'd like to not use test_cmp-alike for the new tests, >>> wouldn't it be simpler to just leave the old ones in place and use your >>> new helper for your new tests? >> >> I'm not sure about this - avoiding changing old tests leads to >> fragmentation in the test suite and even the same file. I find it very >> challenging to read/modify files like this, because there is no longer a >> consistent style for the file, and I have to figure out which is the >> "good" way to write tests. >> >> This suggestion makes sense if there's some qualitative difference >> between the new tests and old ones besides just 'being new'. This isn't >> true for this series, so I'd prefer to keep things consistent. >> >>>> So I don't think there's a correct answer in general. Maybe an >>>> acceptable rule of thumb is that test_cmp is good until it starts >>>> getting in the way of reading and writing understandable tests. >>>> >>>> If we agree on that rule, then for this patch, I think replacing >>>> test_cmp is the way to go, primarily because it lets us ignore the 'old >>>> head' of the branch before the fetch, e.g. in the quoted example.. >>> >>> [...] >>> >>>>>> test_expect_success setup ' >>>>>> @@ -274,13 +277,10 @@ test_expect_success "Recursion doesn't happen when no new commits are fetched in >>>>>> ' >>>>>> >>>>>> test_expect_success "Recursion stops when no new submodule commits are fetched" ' >>>>>> - head1=$(git rev-parse --short HEAD) && >>>>>> git add submodule && >>>>>> git commit -m "new submodule" && >>>>>> - head2=$(git rev-parse --short HEAD) && >>>>>> - echo "From $pwd/." > expect.err.super && >>>>>> - echo " $head1..$head2 super -> origin/super" >>expect.err.super && >>>>> >>>>> ...as opposed to if we just rolled the generation of this into some >>>>> utility printf function. >>>> >>>> we'd still have to deal with $head1 if we use test_cmp. That's fine for >>>> this test, because it's pretty simple, but it gets pretty janky later >>>> on: >>>> >>>> @@ -345,20 +339,13 @@ test_expect_success "Recursion picks up all submodules when necessary" ' >>>> git fetch && >>>> git checkout -q FETCH_HEAD >>>> ) && >>>> - head1=$(git rev-parse --short HEAD^) && >>>> git add subdir/deepsubmodule && >>>> git commit -m "new deepsubmodule" && >>>> - head2=$(git rev-parse --short HEAD) && >>>> - echo "Fetching submodule submodule" > ../expect.err.sub && >>>> - echo "From $pwd/submodule" >> ../expect.err.sub && >>>> - echo " $head1..$head2 sub -> origin/sub" >> ../expect.err.sub >>>> + git rev-parse --short HEAD >../subhead >>>> ) && >>>> - head1=$(git rev-parse --short HEAD) && >>>> git add submodule && >>>> git commit -m "new submodule" && >>>> - head2=$(git rev-parse --short HEAD) && >>>> - echo "From $pwd/." > expect.err.super && >>>> - echo " $head1..$head2 super -> origin/super" >> expect.err.super && >>>> + git rev-parse --short HEAD >superhead && >>>> ( >>>> cd downstream && >>>> git fetch >../actual.out 2>../actual.err >>>> >>>> In this example, we have two $head1 variables in different subshells, >>>> one of which is HEAD, but the other is HEAD^. The reason why we want >>>> HEAD^ isn't obvious (IIRC it's because the submodule upstream is 2 >>>> commits ahead because we add the deepsubmodule in a separate commit), in >>>> my opinion, and I got tripped up quite a few times trying to read and >>>> understand the test. That's a lot of effort to spend on irrelevant >>>> information - the test actually cares about what it fetched, not where >>>> the ref used to be. >>>> >>>> So for that reason, I'd prefer to remove test_cmp for this test. >>> >>> I agree that it's pretty irrelevant, but I also think we'd be throwing >>> the baby out with the bath water by entirely doing away with test_cmp >>> here, there's an easier way to do this. >> [...] >>> Instead let's just test once somewhere that when we run submodule >>> fetching that submodules are indeed updated appropriately. Surely other >>> submodule tests will break if the "update" code is made to NOOP, or >>> update to the wrong HEAD> >>> >>> Then for all these test_cmp tests we can just sed-away the >>> $head1..$head2 with something like (untested): >>> >>> sed -n -e 's/[^.]*\.\.[^.]*/OLD..NEW/g' >>> >>> I.e. let's just skip this entire ceremony with asserting the old/new >>> HEAD unless it's really needed (and then we can probably do it once >>> outside a test_cmp). >>> >>> If you grep through the test suite for "sed" adjacent to "test_cmp" >>> you'll find a lot of such examples of munging the output before >>> test_cmp-ing it. >> >> Makes sense, I hadn't considered this (though I have seen the pattern in >> the test suite, oops). The most compelling argument in favor of this is >> that this could remove a lot of the complexity of verify_fetch_result(), >> which is impeding test readability. >> >>> I.e. none of these tests surely need to test that we updated from >>> $head1..$head2 again and again with the corresponding verbosity in test >>> setup and shelling out to "git rev-parse --short HEAD" or whatever. >> >> I find the converse (we are testing the formatting over and over again) >> less convincing. In these tests, we really are checking for $head2 in >> the stderr to verify that the correct thing was fetched. I'm not >> convinced that we should be relying on _other_ submodule tests to tell >> us that submodule fetch is broken. Which brings me back to the original >> motivation of this patch.. >> >>> >>> That's perfectly fine here, since the actual point of the test_cmp is to >>> check the formatting/order etc. of the output itself, not to continually >>> re-assert that submodule updating still works, and that we get the right >>> OIDs. >> >> which is that these tests actually are continually re-asserting the >> submodule updating works correctly in the different circumstances, and >> since we use the stderr to check this, test_cmp adds unwarranted noise. >> >> But you are correct in that the point of test_cmp is to check >> formatting/order etc. There is value in using test_cmp for this purpose, >> and getting rid of it entirely creates a hole in our test coverage. >> (This wouldn't mean that we'd need to use test_cmp _everywhere_ though, >> only that we need to use test_cmp _somewhere_.) >> >> As it stands: >> >> + test_cmp can improve the readability of the test helpers and >> debuggability of tests vs grep >> +/- test_cmp can catch formatting changes that are hard to catch >> otherwise, though at the cost of being sensitive to _any_ formatting >> changes >> - test_cmp needs some munging to eliminate unnecessary information >> >> so on the whole, I think it's worth trying to use test_cmp in the test >> helper. We may not _need_ it everywhere, but if it would be nice to use >> it in as many places as possible. > > I think whatever you opt to go for here makes sense. I just wanted to > provide the feedback in case it was helpful, i.e. when reading it I > found these conversions a bit odd, wondered if they were strictly needed > etc. > > Thanks! The additional perspective was indeed helpful, thanks!
