selftests: ublk: refactor test_null_04 into separate functions

Encapsulate each test case in its own function that creates the
device, runs checks, and deletes only that device. This avoids
calling _cleanup_test multiple times.

Signed-off-by: Ming Lei <ming.lei@redhat.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
This commit is contained in:
Ming Lei 2026-01-30 00:19:55 +08:00 • committed by Jens Axboe
commit 130975353b