Hey Radhika!

You haven't mentioned the exam name which you want to give after your graduation and also the time it would require to prepare for the test also varies depending on the test, candidates previous knowledge on the subject, study schedule of the candidate and so on. So, it depends on the candidates learning habit, schedules, etc. If you want to know about any specific examination then you may mention it in the comment section because there are exams whose preparation takes more than a year time.