Convert ISTJ to socionics
Your four letters are ISTJ
About eight minutes.
ISTJ does not convert to one socionics type, so this quiz decides between the three it can be: ISTj, ISTp and ESTj. The 20 questions are chosen for your four letters and ask about the places those candidates actually differ, not the places the letters already agree.
ISTJ starts on ISTj here, though the letter-flip rule gives ISTp. The test's starting weights set the order.
Socionics writes the last letter small. It's not your MBTI letter.