The trouble with tests like these, they are by nature overly simplistic. It doesn't diminish the fun of taking them (unless like me you get frustrated with personality quizes because sometimes NONE and other times ALL of the options fit you but you are supposed to choose one!) but it doesn't mean they don't get a fair bit correct. But we are always apt to test differently - not only do my feelings and expressions vary day to day (try hour to hour), but even my recollection of how I was in the past varies with the current state of mind and what I chose to focus on in hindsight.
I do lousy on personality quizes. In high school they gave us a 200 question test to tell us what career would suit us. The test also asked what career you thought you wanted. I answered "singer" (which is what I am). The stupid test told me I was best suited to the career military (I can't even imagine lasting 5 minutes in the military!) or insurance sales (I wouldn't even TRY to last 5 whole minutes selling anything, let alone insurance) and the same test told me I should not be a singer because I am too fond of detail, and singers don't need to pay heed to detail. (Obviously written by no one who has ever had to sing in an opera by Richard Strauss.)
As for Myers-Briggs I would have to say I am an EINFP with a great deal of the other traits too. Seriously. And that's without taking into account all the changes in my style over the years, along the lines of what Vanessa discusses.
Every time I say okay Zerbie, just PICK ONE and say you're that, I read the description and think, "Yes, yes, okay yes this is right, yeah that too, yes, wait - oh my God, I NEVER FEEL THAT WAY!! This is totally wrong!" Every time I think I'm a "type" there is some monumental trait that I have the opposite.
So, kinda sorta INFP and ENFP, but absolutely neither and completely both, and omigosh - this is the same way I talk about my sexual orientation - with a personality like this, how could I *not* be bi?!?!