You should always consider being tested if you change your partner or if you have unprotected sex (without a condom). Men can be screened by providing a urine sample and women can be tested with a simple swab.
If you have symptoms of an infection, such as a rash, spots or unusual discharge you can get a symptomatic screen. This will test for a range of STIs, including Chlamydia, Gonorrhoea, mycoplasma, trichomonas, HIV, Syphilis as well as other tests such as Hepatitis A, B & C, depending on your medical/sexual history.
Most STIs can be effectively treated relatively easily. Treatment is important to ensure that you do not pass an STI on to someone else and to stop you from having any associated medical problems in the future – for example some STIs can affect your chances of having a baby in the future if left untreated