Hi Chandni!

Usually you either go to coaching institute for a mock test series or you can do it online. Another alternative would be to but a book of previous years question papers with explanations.

Hope this answers your question!

Arika (State Head @ Careers360)

You can apply for online test series of allen, aakash and even careers 360 is providing a personalized crash course. 

Or you can apply for offline test series in these coachings. 

Mock test is like a real time examination the more you solved the more you prepare for real examination but what matter most is the level of the questions that you are solving.

You can go to any coaching institute for a mock test series.You can go for allen test series. The questions provided are ncert based and most of them are previously asked questions. 

Many online sources provide quality mock tests for NEET preparation.

Another alternative  is solved previous years questions papers with explanation.

All the best !