erofs-utils: tests: check battach on full buffer block

regression test for
https://lore.kernel.org/r/20210118123945.23676-1-sehuww@mail.scut.edu.cn

Signed-off-by: Hu Weiwen <sehuww@mail.scut.edu.cn>
Signed-off-by: Gao Xiang <xiang@kernel.org>
3 files changed