Making a test tiny roast If I am making a corned beef and after 10 days I want to taste it and make sure I got the seasoning right. If not I'll fix it and let it soak for another few days. 

So I want to cut off a small piece and cook it.  Maybe 4 oz. what would be the best approach for cooking it? Would it follow the normal rules for making a corned beef such as internal temperature which will probably happen pretty fast or does it need a minimum amount of time for some chemical or mechanical processes to happen? Any other ideas?
I make a lot of home cured corned beef so the seasonings are pretty set. When I first started, I didn't try to make a soft tiny roast to test the seasoning, instead I sliced off a thicker slice and cooked in slowly on the stovetop until it was done to my liking then tasted it. I wasn't worried about making it soft and tender when I was testing for seasoning.
One of the best ways to make a roast soft and tender is to use a sous-vide immersion circulator. Set it to your final temperature, let the water heat up,  put the roast in a plastic bag, remove the air and cook until tender. You can find dozens of resources about sous-vide cooking on-line.