t3415: verify that an empty instructionFormat is handled as before
An upcoming patch will move the todo list generation into the
rebase--helper. An early version of that patch regressed on an empty
rebase.instructionFormat value (the shell version could not discern
between an empty one and a non-existing one, but the C version used the
empty one as if that was intended to skip the oneline from the `pick
<hash>` lines).
Let's verify that this still works as before.
Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
Signed-off-by: Junio C Hamano <gitster@pobox.com>