Given that I was hired based on my professors referral to the head of the department, the interview was very brief and informal. The professor already knew most of my skills and qualifications and the interview with the head of the department was just a formality.

The interview was not very hard. Fir about 20-25 minutes, all the questions were related to personality (HR questions), and then they explained about the job description in detail and started with the technical round. A few questions were hard but you just have to be very strong in the basis of the field you are applying for graduate research assistant position.