I don't want to be friends with someone who refuses to get tested for sti's
Is getting tested for STI's a thing that is important to you?
Testing for sexually transmitted infections is a logical step.
Ultimately their choices are their own, but such testing is a moral and value issue and the disagreement is valid. It can be difficult, and sometimes impossible, to maintain a friendship when core values clash.
I'm not respecting their decision to get tested and I won't be friends with anyone dumb enough not to get tested.
It seems like you know who you would prefer to surround yourself with. That said, rather than cutting them off, perhaps you could try to help them understand that getting tested and having regular checkups is important for their health and those of their partners.