Hello, Same problem here after yesterday's upgrade. The 0.122~a.test initramfs-tools and initramfs-tools-core packages mentioned by Ben at <https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=811479#19> allowed my system to boot, thank you!
(along with the Debian jessie installation DVD in rescue mode, its option to automatically assemble RAID arrays, followed by mounting the /, /usr and /var filesystems of my normal system at temporary mount points, chrooting into the temporarily-mounted root before running dpkg -i the_deb_files [maybe simply booting with the previous kernel to install the test packages would have worked, too?..]) Regards -- Florent