Re: [PATCH 1/2] t/t1417: test symbolic-ref effects on ref logs

From: Kyle J. McKay <mackyle@gmail.com>
Date: Jan 30, 2021, 23:26 UTC
Message-ID: <81AEEED6-26EC-4F32-AA65-B028435D812D@gmail.com>
In-Reply-To: <xmqqa6sqp827.fsf@gitster.c.googlers.com>

On Jan 30, 2021, at 11:56, Junio C Hamano wrote:

Show 9 quoted lines

>> Add a new set of tests to exercise and demonstrate this change
>> in preparation for correcting it (at which point the failing tests
>> will be flipped from `test_expect_failure` to `test_expect_success`).
>
> We usually prefer not to do the two-step "expect_failure first and
> then in a separate patch flip that to _success", as it makes it hard
> to see the "fix" step (because the change in the test would be shown
> only 3 lines before and after _failure->_success line, and what the
> test is doing cannot be seen in the patch by itself).

I'm having a bit of trouble parsing that into expectations. A little help please.

Given the scenario that a bug is found that is not being caught by a test (irrespective of whether or not the outcome of this particular series discussion results in it being determined to be a "bug").

Further, if the fix is simple enough that it warrants only a single patch, what is the preferred order of patches then?

I would like the patch series to demonstrate:

1) that the test actually catches the bug (in case it comes back in  
the future)
2) the fix isolated (as much as possible) in a patch distinct from the  
test
3) that the test now passes, preferably with minimal changes to be  
sure that it hasn't accidentally been rendered ineffective

All the while, at no point after commits for (1), (2), or (3) is the test suite allowed to generate extra failures (that are not marked "expect failure").

patch 1/2 accomplishes (1) patch 2/2 does both (2) and (3)

Are you suggesting that (1) just be omitted? Or that it be modified so that it's an "expect success" patch? But then (2) would break it and introduce a failing test into the test suite. Should (2) then just flip the test from test_expect_success to test_expect_failure and then a separate commit flip it back to test_expect_success along with the minor change to the test itself to make it start passing again? In that case, there's always a risk that changing the test itself could accidentally make it no longer detect the problem anymore and just always succeed even if the problem comes back.

Without an initial expect_failure step (1), there's no commit in the repository that can demonstrate that the test actually catches the problem.

I understand that when new code is added, the tests come after, but it seems to me that when fixing a pre-existing problem, the test that demonstrates the problem should come first and be an expect failure since it is considered to be a problem.

What exactly is the order of test/fix changes that you're expecting to see here?

Thanks.