Re: [PATCH] Re-re-re-fix common tail optimization

[Junio C Hamano <gitster@pobox.com>]

Junio C Hamano <gitster@pobox.com> writes:

>>> +test_expect_success 'diff -U0' '
>>> +
>>> +	git diff -U0 | sed -e "/^index/d" -e "s/$z2047/Z/g" >actual &&
>>> +	diff -u expect actual
>>
>> Aren't we using "git diff" for the second diff there nowadays?
>
> Some people seem to think that is a good idea, but I generally do not
> like using "git diff" between expect and actual (both untracked) inside
> tests.  The last "diff" is about validating what git does and using "git
> diff" there would make the test meaningless when "git diff" itself is
> broken.
>
> This is especially so because comparison between untracked files is a
> bolted-on afterthought and I am least confident about among the
> codepaths in the whole "git diff" (it is not even my nor Linus's code).

Side note.  The "confidence" I am talking about the above is not about
the correct-working of the current code.  It seems to work fine.

It is about the fact it was bolted on rather than designed in from the
beginning---it is much likely to subtly break than other parts that are
much more integrated when you change seemingly unrelated thing like
git-dir discovery and rename detection.

IOW, the confidence is about the fixability/maintainability when
somebody breaks it.