Re: [PATCH 1/2] t7002: set test prerequisite "external-grep" if supported

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

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

> Nguyễn Thái Ngọc Duy  <pclouds@gmail.com> writes:
>
>> Add another test to set prerequisite "external-grep" if the current
>> build supports external grep. This can be used to skip external grep
>> only tests on builds that do not support this optimization.
>
> Thanks.  We seem to spell our prerequistes in a single-word, all-caps, so
> I'll change this new one to EXTGREP in both [1/2] and [2/2].

Sorry, but I had this "Sheesh, why didn't I think of that earlier before
wasting Nguyễn's time" moment.

Why don't we just test what we _want to_ test?  After all what a67e281
(grep: do not do external grep on skip-worktree entries, 2009-12-30)
wanted to make sure was this:

    "git grep" (without --cached) should grep from the index for paths
    that are marked as skip-worktree.

So how about writing some string that does not appear in the version in
the index in the work tree file, and run "git grep" to make sure it
doesn't find it?

Yes, some implementations/builds of "git grep" may not even try to cheat
and run external grep and for them the test _should_ succeed (but your
logic to check with ce_skip_worktree() in grep_cache() may be broken by
later patch while you are looking the other way), and some will try to
cheat and the fix was about not letting them.

So by writing the test to check the desired outcome, instead of writing it
for the particular implementation of using external grep optimization, you
will catch both kinds of breakages.

Perhaps something like this (untested, of course)?

test_expect_success 'strings in work tree files are not found for skip-wt paths' '
	no="no such string in the index" &&
	test_must_fail git grep -e "$no" --cached file &&
	git update-index --skip-worktree file &&
	echo "$no" >file &&
	test_must_fail git grep -e "$no" file &&
	git update-index --no-skip-worktree file &&
	git grep -e "$no" file
'