Here's the quick rundown based on my understanding.

In straight porn, studios require performers to regularly get tested for STDs, including HIV. Condoms are sometimes, but rarely used.

In gay porn, it varies. For a long time, what was considered standard was that condoms were used, but HIV testing was not. The reason for this is partially political. Post AIDS epidemic, gay men were sensitive about anything that could make them feel "quarantined" or singled out like mandated testing. Which, I know, sounds dumb. The solution gay porn producers used was even dumber -- treat everyone on set as if they already have HIV. Condoms for everyone.

Some studios took an even dumber approach -- no testing or condoms are required, but serosorting was used. Meaning that people who "knew" they were HIV positive would work with other performers who were HIV positive, and performers who "knew" they were negative would work with other performers who "knew" they were negative.

As you might expect, the fatal flaw with this is that it requires people to take the initiative to get tested on their own and doesn't take in to account that they have sex with other people off set.

Why might this be doubly concerning for a porn actress? As of 2010, the CDC estimated that 1 in 5 gay men are HIV positive, but that 44% of them don't know they have it. That figure is for the general population, not for workers in an industry where sex is had at a higher than normal rate with a multitude of partners, testing is rarely performed, and condom use depends on the studio.