Well, online exams are not tough, but it depends upon the subject for which the online test is to be performed or the amount of knowledge that a student holds in a particular subject. There are some online tests like Mensa, which is related to general knowledge. On the other hand, the GRE test is an exam framed to test vocabulary, analytical and mathematical skills. These exams can be complex and easy, but tests like CCIE are tough to perform and are carried by CISCO Network.