What do I do if I'm being asked to be a witness for both the plaintiff and the defendant in a small claims court?

I am being asked to be a witness on both sides in small claim court. I am only on one person's side however the other one thinks that I will testify on their behalf as a witness. What do I do? I told the person who side I'm on they don't need to subpoena me, I will show up on their behalf but what if the other person subpoenas me? What do I do?