How to create and mount a loop-device with guestmount?

The goal is to test the out of disk space condition.

Creating an image:

dd if=/dev/zero of=test bs=1024 count=10000

Mountpoint:

mkdir mountpoint

Mounting fails:

guestmount -a test -m/dev/sda mountpoint

mount: wrong fs type, bad option, bad superblock on /dev/sda

Is there a need to create an fs? How to make the image usable?

(without the root user)