How can I tell if my engagement ring is real?

The ring my boyfriend gave me doesn't have any karat sign or number, my boyfriend said that he had it customized and that's probably why but I don't think that's true, then again I don't know alot about engagement rings. It's a white gold ring with a cubic zirconia as the main stone and little diamonds on the bottom part, he said he got two rings welded so we could use that ring to get married too.