One of my friends took the entrance test for integrated Ph.D. program in Physics at IISER Mohali. His experience throughout the entire process is discussed below in brief. 

• The selection process includes a written test followed by an interview. The written test takes around 60-90 mins. Students who clear the test are shortlisted for the interview. 
• The question asked in the test are objective type. The difficulty level is moderate. If you have a thorough understanding of your undergraduate subjects, you can easily solve the paper in time. You will need to wait for a couple of hours for the result to be displayed. 
• The interview will last for about 20-40 mins. The interview panel usually consists of four faculty members. They usually ask basic questions to test your fundamental knowledge of the subject. If you don’t know the answer to a particular question, it is better if you say it clearly, rather than guessing.