Precisely. It's a shallow test. Sorry Alamogirl. It will take pages of y/n/maybe queries to divine my true personality.
I on the other hand will take some introvertive activity over parties a good 90% of the time. The "I" is a true result. The "S", if I understand it correctly, is also a true result to some extent-- it depends on the context. "T" rather than "F" is true. "J" I don't understand however.
The flip side of "J" is "P". Judging vs. Perceiving. Do you have opinions about what you see and hear? Or do you see and hear things and think, "Oh that's nice."?
J is part of the Judging/Perceiving dimension. Do you prefer closure or keeping your options open? Do you prefer to make judgements (decisions) or to take in and absorb information (perceive)?
J/P also indicates which of your functions is extraverted (used in the external world). The functions are Sensing, Intuiting, Feeling and Thinking. Sensing and Intuiting are different ways of perceiving; Feeling and Thinking are different ways of making decisions.
If you are a "J" then it means you prefer making decisions, so your decision making function is the one that is extraverted (used in the external world). In the case of an ISTJ, that would be thinking. In the case of an INFJ, that would be feeling.
If you are a "P" then it means you prefer taking in information, so your perceiving function (S or N) is the one that is extraverted. In my case, as an INFP, that would be iNtuiting.