Motor #2

Hi all. This sub has helped me out a lot to feel more comfortable flying. However I am at the gate on the plane with a delay and I was wondering if someone could explain to me what this all means. The pilot said they have to run motor #2 for 5 minutes then have the mechanics inspect it and they will either sign off on it or we’ll get another plane. Can someone please help me understand why they have to run motor #2 and what could be wrong? The pilot apologized for the delay and said “safety fist” which I really appreciated but it still has my anxiety taking over. Thanks in advance!