No test that I know of but then it really doesn't matter very much, either. There are some woods which have sap and that can cause trouble of various types. Sap is what causes color problems so it is good to get dry wood. There are a few limited type/species of wood which have toxic sap. Cedar is semi-famous as one to avoid but when the sap is gone, I often use it.
So I would say there is a very good chance that the wood itself is safe due to the obvious age and lack of sap left in it. A few like hickory, pecan, or walnut may still color the water, though. Of all the trees, your odds are really good but then it is always prudent to take some care as we don't know what may have happened to the wood while it has been out in nature. Things like oil and pesticides are all over the place now so I take some care to clear those and any bugs fungus, etc. I just like to start with a clean plate to avoid any nasty surprises to figure out?
One good way is to do a bleach soak. When I have an empty tank, I use it as a handy container and just do the whole things, tank, wood and all.
A container to hold the water and a 1/2 to full cup of plain, unscented, uncolored bleach and soak overnight or 8-10 hours to give it plenty of time to soak into all the tiny cracks and crannies or until I get back around to it. I try to do it outside to avoid the chlorine gas smell in the house.
Soaking too long never hurts while too little may not do a bug that has borrowed really deep.
Watch not to splash the bleach on your clothes as it does react with all organics and that includes clothing!
There is zero chance that the chlorine soaks in to stay there as it does react with wood until one or the other is gone. No magic that soaks in and only reacts with selected organics!
Expect the wood to turn white, due to the reaction but not to worry as the color comes back in pretty short order when we start using the wood. That white color is why mama used it on our diapers before we switched to paper.
Rinse the wood to dilute any leftover chlorine and then let the rest blow away as it returns to gas form as soon as it can. Close the bottle tight or it goes bad!
When all the smell is gone, the wood is sterile and good to use. There may not be anything on the wood but then I still like my dishes washed and steril before I use them and feel much the same about my tank stuff.