SZEDER Gábor [off-list ref] writes:

quoted

The conversion was generated using a grep-assertion linter
(greplint.pl, added in the following commit) to identify bare
grep calls at command position.  To reproduce:

    # Step 1: mark bare greps that should not be converted
    sed -i '/! grep "$m" \.git\/packed-refs/s/$/ # lint-ok: file may not exist (reftable)/' \
        t/t1400-update-ref.sh
    sed -i '/! grep dirty file3 &&/{/lint-ok/!s/$/ # lint-ok: file may not exist after --quit/}' \
        t/t3420-rebase-autostash.sh

I think in this case checking the file3's contents is wrong, because
at this point file3 should not exist in the first place.  I've sent a
patch to fix this long ago, but apparently didn't manage to follow
through back then.

  https://lore.kernel.org/git/20211010172809.1472914-1-szeder.dev@gmail.com/ (local)

Thanks.  I guess the test_grep can be extended to catch this case,
where 

    test_grep ! -e pattern1 -e pattern2 file

does not find any hits, but only because 'file' is missing, as an
error, just like "test_must_fail git foo" that segfaults is flagged
as "yes, it fails but that is not the kind of failure we expect".