While my response is probably not as good as the HN, I can tell you that on average I have a condom "situation" about 2 times a year. My standard response is to show the client the results of my most recent testing (to ease their mind a little bit) and ask that they get tested as well, as a courtesy, and email me the results. In my experience the clients have been willing to do this, I'm not sure if I am out of line asking...but I think it gives people peace of mind.
Moreover, there are risks when a condom breaks...especially for the SP if the client "finishes" sans condom...there is risks also for "skin to skin" stuff like HSV2/1 etc. HIV and Hep C transmission is possible, but probably not likely, because from what I have read the risks of a single incidence of unprotected heterosexual vaginal sex (as is the example with condom breakage) are about 1/1000, and even less for female to male transmission.
So yes, always better to be safe, but a broken condom is not always the end of the universe. It will probably kill you with anxiety before anything else.
Xo - Chanel - Xo