The presence or lack of symptoms isn't what determines the need for STD testing in most cases, as a number of infections often don't cause quick or easily noticed signs.
Oral sex is considered much less risky for most STDs, including HIV, than vaginal and anal intercourse, but of course there is always some risk if someone performs oral sex on an HIV-positive partner. Sometimes testing is good for peace of mind, even if the risk isn't overwhelming. Here's what CDC says in terms of who should be tested:http://www.cdc.gov/hiv/topics/testing/resources/qa/be_tested.htm#testedShould I get tested?
The following are behaviors that increase your chances of getting HIV. If you answer yes to any of them, you should definitely get an HIV test. If you continue with any of these behaviors, you should be tested every year. Talk to a health care provider about an HIV testing schedule that is right for you.
Have you injected drugs or steroids or shared equipment (such as needles, syringes, works) with others?
Have you had unprotected vaginal, anal, or oral sex with men who have sex with men, multiple partners, or anonymous partners?
Have you exchanged sex for drugs or money?
Have you been diagnosed with or treated for hepatitis, tuberculosis (TB), or a sexually transmitted disease (STD), like syphilis?
Have you had unprotected sex with someone who could answer yes to any of the above questions?
Hope this helps.