Have tested as INTP, ISTP, and INTJ (mostly INTJ). Never tested INFJ in any of the online assessments that I have completed (about a dozen or so).
Based on the online tests, I was convinced that I was an INTJ for several months. After hanging out on another forum, I realized that I did not have the personality that is so typical of that type.
Working in the tech field, I spend a lot of time with introverted thinkers (both NT and ST varieties). While I admire their intellectual ability and lightning fast wit, I always feel like an outsider. In some ways inferior, yes. I can't crank out source code like a dominant Ti/Te.
OTOH, Ni/Fe has been a powerful asset. Computer systems are little more than a pitiful attempt to clone some facet of human intelligence. My NT/ST techno comrades always look for a system failure first when troubleshooting. I look for the human element.