My opinion differs from those above. I don't do any wet strand tests, and to be honest, I never heard of the term until now and I've been on this journey for several years. But, sometimes you miss things.
I second the person above who said "listen to your hair." I usually do a protein treatment about 1-2x a month, and definitely after I flat iron. I usually know my hair needs protein when it is overly frizzy and won't style in the normal manner b/c the frizz takes over. It probably varies from head to head. But as a natural, I need moisture way more than protein, but I do need the occasional protein treatment too, especially after using heat.