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

>  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
>  '
>