I've not tested it, but it should expand just like anything else. The effect would broadly be that running "rm *" in the directory would recurse into subfolders without warning.
You can spin up a droplet and use the online shell tool or ssh in (very easy when you've set up a cert as the droplet can have the cert setup automatically).
Then you can mess about with a droplet as much as you like, virtually speaking. Once you're done then use the control panel to destroy the droplet - it costs a few ยข a day and if you don't have a droplet in use (which means active or paused; preserving images is cheaper but non-zero) then you don't pay anything.
Basically sign up and have a year of uptime to mess with a full install of various OS with no charge.
Make sure you don't write "rm -rf /*" in the wrong terminal!