I'm in monogamous LTR, and we got tested together only once, one year into the relationship, in order to discard condoms.
It means we trust each other on our life, literally.
But, seriously, the trust is not about never ever 'failing', it's rather that it would not be a big issue for either of us to tell if we did.
We might not be the norm, as we choosed a purely monogamous relationship while being blessed with no jealousy.
Now to answer the post, I would no see myself practice unsafe sex with anyone at the beginning of a relationship. Testing doesn't protect you.
I think it's a mature and reasonable discussion to have with a new sex partner, alongside hiv status, other mst (hepathisis etc..), and the level of safe sex and health control wich makes you both feel comfortable. I would have hard time to trust someone trying to avoid those topics today or finding them irrlevant.
If you want to bareback at one point, be sure both of you are able to confess if you have a side affair. To many men and women get infected because guilt and fear to lose your lover make some guys have unexpected sex without protection, then say nothing, hope they did'nt get infected and keep having unprotected sex with their reguolar partner.