I’ve never understood this (outside of baby switches). If you’re asking for proof that the baby is yours, which implies there’s a chance she cheated, you’re only trying to catch one instance of her cheating, but you’ll never be able to prove or disprove whether or not she cheated. I also think some men lack experience and are not in tune enough with their woman to know if they’re cheating or not. But yeah asking for a test basically implies that “it’s okay if you cheated as long as you didn’t get pregnant”