Unexpected pregnancy...surprise announcement or no?

First of all, I’m not pregnant to my knowledge. But my period is a few days late and I’m going to take a test. If I am pregnant, its going to be a huge shock to my fiancé. I know he is going to be super stressed out, even though I know he will support me and love his baby. But I want to announce it in a fun way! I wanted to surprise him with a cute “hello daddy” onesie or something like that on our upcoming trip, but I’m afraid he will just freak out. Should I just tell him as soon as I take the test?