using FreeBSD to create a completely new OS

[Alexander Yerenkow]

If you consider VirtualBox for automated tests, you should make some
testing life cycle.
I'd recommend to you:

1. create sparse file (truncate -s 1G for example)
2. mdconfig -af file (produced md0)
3. work with md0 as if it was real hw disk (write boot sectors, fs, etc),
then destroy md0 (mdconfig -du 0)
4. create vmdk for file (
https://github.com/yerenkow/freebsd-vm-image/blob/master/freebsd-firmware/create-scsi-vmdk.sh
-- this helps me create vmdk for raw file and feed them to
VmWare/Virtualbox just fine)
5. boot VirtualBox using cli (and run some tests).

I had some experience in running in-virtualbox-os tests a while ago, but
there was real OS there, and not test one.
Hope this helps.

-- 
Regards,
Alexander Yerenkow