The title phrase is better.Or shall i say, "successful sitting" in exam? Which is correct? Or what's the best expression?
That's fine in BrE - you can take or, more formally sit an exam(ination). After the results come out, you know whether you have passed or failed it. What L7 may be needing is some form of official 'confirmation of attendance'. The candidate could then show this certificate to, for example an employer who had granted leave for the examination, confirming that s/he had indeed attended/sat/taken the examination.Then "I took the exam" would put you at the site of the exam. (But it seems the OP wants BrE.)
I would have thought that proof of identity was more relevant than confirmation of attendance in such cases.Some exams, like IELTS in some countries, have a problem with fake candidates.