If you are searching for Free Online Test Series for competitive or entrance exams, then you must visit: Practice Guru.
It is India's only site to provide Online tests for so many exams and also gives you facility to order a CD for using without internet! You will find tests on every chapter/ topic of the subject, you will find MOCK tests as well as full syllabus tests.
The pattern is always new and updated. Solutions are readily available and you can compare your performance on All India Level!
The interface of online test looks alike the actual exam (if conducted online). Else, its always good to practice as much as you can before the actual exam.
Interface of Online test
To try free tests, visit http://practiceguru.in/OnlineTestSeries.aspx