Very often infections transmitted sexually do not cause symptoms so may go unnoticed.
However, if there has been any risk it is easy to test using swabs from possibly infected sites. Men can usually be tested by a urine test for Gonorrhoea and Chlamydia. Also, Mycoplasma now warrants testing in symptomatic patients though the best swab is not always available.
A blood test for HIV and syphilis completes the routine screening