Re: [PATCH v3 2/2] tests(mingw): avoid very slow `mingw_test_cmp`

From: Junio C Hamano <gitster@pobox.com>
Date: Nov 18, 2022, 23:19 UTC
Message-ID: <xmqqr0xzkfz8.fsf@gitster.g>
In-Reply-To: <221114.86pmdplbs5.gmgdl@evledraar.gmail.com>

Ævar Arnfjörð Bjarmason <avarab@gmail.com> writes:

Show 12 quoted lines

> IOW this bit in t/README:
>
>  - Don't use '! git cmd' when you want to make sure the git command
>    exits with failure in a controlled way by calling "die()".[...]
>
> So, before this series a test like this on Windows, with
> GIT_TEST_CMP=mingw_test_cmp:
>
> 	! test_cmp foo bar
>
> Would only succeed if "foo" and "bar" weren't identical, now it'll also
> succeed if 'git diff --no-index' happens to segfault on those inputs.

Well "! test_cmp" is wrong anyway, because it _expects_ two files are the same and gives more detailed diagnosis when they differ by giving "diff" output.

If you expect them to be different, "! test_cmp" would give "detailed diagnosis" in the wrong case, i.e. the outcome is what we expect.

So the caller must do "test_cmp !" whether the underlying implementation of test_cmp uses "diff -u" or "diff --no-index".