How do I test the electric differential lock on my Daihatsu?

After activating the differential lock, drive slowly on pavel roads and make a full turn either way. If the differential lock is working, the vehicle would tend to feel as if the brakes are dragging.

Thanks. It works.
On sand I could not feel the difference with it on. I have not been in a situation yet where I got stuck with it off and by switching it on got out.