Subject: Re: [PATCH 0/8] Resend of GIT_TEST_PROTOCOL_VERSION patches

From: Ævar Arnfjörð Bjarmason <[email-masked]>
Date: Wed, 06 Feb 2019 23:20:32 +0100

On Wed, Feb 06 2019, Jeff King wrote:

> On Wed, Feb 06, 2019 at 10:52:15PM +0100, Ævar Arnfjörð Bjarmason wrote:
>
>> > I wonder if it would be more obvious what's going on if we instead had a
>> > prereq like:
>> >
>> >   test_expect_success !PROTO_V2 'ls-remote --symref' '
>> >      ...
>> >   '
>> >
>> > and just skipped those tests entirely (and in a way that appears in the
>> > TAP output).
>> >
>> > I think it would also future-proof us a bit for v2 becoming the default
>> > (i.e., when GIT_TEST_PROTOCOL_VERSION being blank does mean "use v2").
>> >
>> > I dunno. It probably doesn't matter all that much, so it may not be
>> > worth going back and changing at this point. Just a thought.
>>
>> So far we've had the convention that these GIT_TEST_* variables,
>> e.g. the one for the commit graph, work the same way. Thus we guarantee
>> that we get (in theory) 100% coverage even when running the tests in
>> this special mode. I think it's better to keep it as-is.
>
> But what's the point of that? Don't you always have to run the test
> suite _twice_, once with the special variable and once without?
> Otherwise, you are not testing one case or the other.
>
> Or are you arguing that one might set many special variables in one go
> (to prefer running the suite only twice, instead of 2^N times). In which
> case we are better off running the test (as opposed to skipping it), as
> it might use one of the _other_ special variables besides
> GIT_TEST_PROTOCOL_VERSION.
>
> I can buy that line of reasoning. It still doesn't cover all cases that
> a true 2^N test would, but that clearly isn't going to be practical.

Maybe I'm misunderstanding what you're proposing, but as an example,
let's say the test suite is just these two tests:

    test_expect_success 'some unrelated thing' '...'
    test_expect_success 'test protocol v2' 'GIT_TEST_PROTOCOL_VERSION=2 ...'

And GIT_TEST_PROTOCOL_VERSION=0 is the default, let's say I want to test
with GIT_TEST_PROTOCOL_VERSION=1 for whatever reason,

I'd still like both tests to be run, not just 1/2 with
GIT_TEST_PROTOCOL_VERSION=1 and 2/2 skipped because it's explicitly
testing for the GIT_TEST_PROTOCOL_VERSION=2 case, whereas I asked for a
GIT_TEST_PROTOCOL_VERSION=1.

IOW the point of these tests is to piggy-back on the tests that *aren't*
aware of the feature you're trying to test. So
e.g. GIT_TEST_COMMIT_GRAPH=true should run our whole test suite with the
commit graph, and *also* those tests that are explicitly aware of the
commit graph, including those that for some reason would want to test
for the case where it isn't enabled (to e.g. test that --contains works
without the graph).

Otherwise I can't say "I care more about GIT_TEST_COMMIT_GRAPH=true than
not", and run just one test run with that, because I'll have blind spots
in the commit graph tests themselves, and would then need to do another
run with GIT_TEST_COMMIT_GRAPH= set to make sure I have 100% coverage.