If a new prophet of the Lord were to come forth, what criteria would we use to determine if they were actually a prophet?

I know that John the Baptist is the last prophet of the old covenant, but he isn’t the last prophet of the Bible. John the Beloved (or whoever wrote Revelation) is the last biblical prophet, and that prophecy has yet to come to pass. Obviously a prophecy doesn’t need to be completed before someone is regarded as a prophet, so what exactly is the criteria?