I taste test! Just depends on how you like them.
There are many, many ways to do brisket and what I described is just one of many. It's what I like to do but a lot of members will offer suggestions and I think you should take all the advice and develop your own method! Remember as long as you are safe there is no right way, just different ways.
Some people take the whole packer to 165 wrap it, return to smoker to 200 - 210 and pull it, some take the flat to 170 - some 190 for slicing, some to 205 or so and pull that.
Remember if cut at too low a temp it can be tough so I find foiling with finishing sauce early (160?), allowing it to get to the higher temp, then some time in the ice chest helps to tenderize it. You just don't want it to go to high or you won't be able to slice.