A simple smoke test might be to run something like
sudo dd if=/dev/sda of=/dev/zero &
sudo find / >/dev/null 2>&1 &
sudo grep -r . / >/dev/null &
and run fstrim-all in parallel. You can of course do the original thing of setting up a schroot and sbuild libreoffice in that (or just "sudo apt-get build-dep libreoffice; apt-get download -b libreoffice" on your workstation if you don't mind it getting cluttered with lots and lots of build depends).