Questions to discern if you are talking to an INTJ:
"If Julius Caesar were assassinated today, how would it happen?"
The answer: It wouldn't or shouldn't happen again, in an advanced, civil society. (This isn't true in every SINGLE case *ahem, but it's the popular opinion. It's the right thing to say to not draw attention to yourself, for certain, and that's INTJ all over.)
If the person answers, describing the manner of assassination, however detailed and meticulous and completely imagined, they are most likely not an INTJ. INTJs aren't braggarts, and seek rarer fruits. Higher branches, away from others, but rarely lead the way by choice. And they might not let everyone know where the best fruits are either.. then there would be no secret fruit! Hell, why let ANYONE ELSE know about secret fruit?