I've been running this test and it works fine.
Just fill a plastic water container with water and turn it upside down in a
dish with a vertical lip. Support the bottle but put a small spacer between
the bottle opening and the base of the dish to allow water to escape.
get hold of some capillary matting and sit the plant pot on this, then take or
cut a strip of capillary matting and place one end in the dish with the lip.
Or you could put one end of the capillary strip in the soil but I have not
tried this method.
It could be possible to market this but I have used this method in a cold frame
and fifty or so plants over some years.