What books should one refer to to crack the IISER aptitude test?

After doing some research online, here are some pointers that might help you answer your question. 

• Prepare off-track topics. 
• Questions can come from the unnoticed chapters in the NCERT textbooks. 
• You can refer to the NCERT books and the JEE main books for preparing for the aptitude test. 
• JEE MAIN and NEET sample papers can also be practiced. 
• NEST questions are available online every year for smooth preparation of the examination. 
• After solving the NCERT book, you can refer to Halliday, Resnick and Walker, H.C. Verma, J.D Lee, and R.D. Sharma.
• The reference books will have a strong involvement in your preparation if pursued relentlessly.

The questions in your aptitude test should be solved with confidence. There should be no random guessing and overall knowledge and accuracy is important.