I'm INFP - first tested via a very long test on a program for
  MS-DOS back in 1993. Took it a few times more on the new
  Internet. Results were consistent. One day I challenged myself
  to mimic each type. Took about a year. The test is long and I
  had other stuff to do as well (like work). But one day, I
  succeeded. Now, i can't take the test anymore. Of course, it's
  only supposed to be once.