In Tennessee law if the husband dies and there is not a will and there is a wife and one adult son, does the wife get the sole inheritance or the estate or does it get split between the wife and the only child they had?

Welcome to AMHD. Maybe this will help:
31-2-104. Share of surviving spouse and heirs.
(a) The intestate share of the surviving spouse is:

(1) If there is no surviving issue of the decedent, the entire intestate estate; or

(2) If there are surviving issue of the decedent, either one-third (1/3) or a child's share of the entire intestate estate, whichever is greater.
Tennessee Intestacy Laws

By all means, consult an attorney in the state of Tennessee.

I believe the wife gets it all, unless a will states differently.

If the wife does the proper thing, she would indicate in her will, the wishes of the deceased spouse and herself, regarding what would go to the adult son upon her passing, based upon any discussion of the subject when both were still alive.

Definitely an opinion, not a guaranteed correct answer.

First a lot will depend on how things were deeded, and how bank accounts were set up. If done properly, house deeds are done with right of survivialship so the spouse gets it without any estate or probate, The same with bank accounts, For example when my dad passed, there was no need for probate, every item was held in joint ownership

So you will need ( and should have had before it happened) a good estate attorney to review things and see what will or will not have to be part of the estate