I do very little thinking about this actually.
It's so obvious it can hurt
I just make sure that there's some air exchange, but not much, I'd pop one end of the lids on this test.
Also, you do not want the water to cover the leaves at all.
It's just a terrarium. Nothing more.
But you use sediments that can work once you fill the tank up later.
If grow out is the only concern, those simple plant seedling trays work great for any type of foreground type plant, simply keep in a warm area that gets decent partial light.
This is not rocket science, it's very simple.
So you can grow out whatever you want for the most part.
ADA soil is not expensive, nor fancy.
Cost the same as Flourite, less than EC etc.
Mud works also.
Garden soil: sand: peat at 1:1:1 ratio works well for most plants.
Water should not dry up fast, you should add water about once every few weeks.
Think terrarium, but with aquatic plants and a tank you flood later.
If all you want to test is sediments, then the little tupperware test work fine.
Make sure you do several replicates of each type of soil/sediment, do not assumne with a replicate of one, you can make any real conclusion.
It's not hard to run 5 replicates of 5 soil/sediment types, the cheapy semi disposable type of tupperware/Glad etc containers are really cheap, maybe 1.50$ for 4.
So for 10-20$ you can do it if you have the room and space near a window or if it's warm outside.
Then you can grow, or keep a small amount of HC, Hair grass, Utric, Gloss etc without much work. And if you need to grow it out well to do a larger tank, you can for peanuts and some time.