yeah, they do extensive hiv and std testing. the tests are almost immediate for results nowadays.
the only problem with tests, is that HIV has a long period of hidden activity, while it can't be detected. and this period is quite long (about 6 months if I am not mistaken) That's why, for example, blood that was taken from donors gotta be sustained for that period in a depository, and after that again tested for virus. Only after that procedure donor-blood can be used for transfusion to other people.
So, of course, tests on a regular basis are good protection from the diseases, but some probability still exists. So, those who are involved in the industry can rely only upon their corporate culture, cuz people gotta understand that with such a job you have to be very accurate in your everyday sex life.
But, all in all, when it comes to watching I prefer to see sex without condoms. And by the way, what could you do with cumshots in the mouth? It is very important constituent of porn. And in case of infected actor, cum will contain HIV virus.