Re: [PATCH v4 2/2] interpret-trailers: add option for in-place editing

> Subject: test-lib: clarify and tighten SANITY
>
> f400e51c (test-lib.sh: set prerequisite SANITY by testing what we
> really need, 2015-01-27) improved the way SANITY prerequisite was
> determined, but made the resulting code (incorrectly) imply that
> SANITY is all about effects of permission bits of the containing
> directory has on the files contained in it by the comment it added,
> its log message and the actual tests.
>
> By the way, while we are on the subject, POSIXPERM is more about "if
> we do chmod, does filesystem remember it so that ls -l reports the
> same?"  Output from "git grep POSIXPERM t" shows that some users of
> it also assume that it requires "we can make something executable by
> doing chmod +x and unexecutable by doing chmod -x" (and that is
> fine--running tests as root would not make an unexecutable file
> executable).  The tests that require POSIXPERM but not SANITY can be
> run by root (I am not saying that running tests as root is safe or
> sane, though) and are expected to produce the same result as they
> were run by a non-root user.
>
> Signed-off-by: Junio C Hamano <gitster@pobox.com>
> ---
> +# SANITY is about "can you correctly predict what the filesystem would
> +# do by only looking at the permission bits of the files and
> +# directories?"  A typical example of !SANITY is running the test
> +# suite as root, where a test may expect "chmod -r file && cat file"
> +# to fail because file is supposed to be unreadable after a successful
> +# chmod.  In an environment (i.e. combination of what filesystem is
> +# being used and who is running the tests) that lacks SANITY, you may
> +# be able to delete or create a file when the containing directory
> +# doesn't have write permissions, or access a file even if the
> +# containing directory doesn't have read or execute permissions.

>  test_lazy_prereq SANITY '
>         mkdir SANETESTD.1 SANETESTD.2 &&
>
>         chmod +w SANETESTD.1 SANETESTD.2 &&
>         >SANETESTD.1/x 2>SANETESTD.2/x &&
>         chmod -w SANETESTD.1 &&
> +       chmod -r SANETESTD.1/x &&
>         chmod -rx SANETESTD.2 ||
>         error "bug in test sript: cannot prepare SANETESTD"
>
> +       ! test -r SANETESTD.1/x &&
>         ! rm SANETESTD.1/x && ! test -f SANETESTD.2/x
>         status=$?