Maybe?

HIV transmission is not so easy; last I checked, the rough odds of transmission from a single act of unprotected vaginal sex with a HIV+ partner was around 1 in 500.

If the test is 99% accurate, and your partner isn't in an obvious high risk group, it may push the odds into "less risky than other behaviors you commonly accept" territory.

For point of reference, condom use only decreases the risk by a factor of 10. Possibly less: https://www.catie.ca/en/fact-sheets/prevention/condoms