There are many sites which gives opporturnity to do mock test but career 360 is better. From first onwards im preparing according to career 360

Hi Aspirant,
There are many sites which provide online mock tests for JEE MAINS and you can easily find it out using Google.
Also,try to appear for the mock tests by the NTA to have a proper exam feel.Also,solve previous years papers because it introduces you to the pattern the best.
Hope this helps.