Hii

No site or app can provide you with free mocktests for JEE and BITSAT. 
You can use entrance360. This platform provides you with a lot of study materials, sample papers, previous papers, a proper timetable for your help, guidance, and is pretty much affordable.
Here i am providing a link for the same. You can refer to the link and check this site for more details.
https://www.entrance360.com/
This is a complete online coaching package for best guidance for any of the entrance exam

Thanks!