Thanks for your post. Condoms breaking is a quite a common problem (more common than people would usually believe) and what you should do next depends on a lot of different factors like the type of sex you were having and each person's STI status.
I've found a few links below that might help you identify whether you need to go for a test. I can't recommend the urgency of your visit, as I don't have a lot of information about the type of sex you had or with who, and in some cases you're best going right away. However, it's generally recommended that if you've had unprotected sex, that you head to an GUM clinic for a checkup. Try giving the below links a read and you can decide when you should go for yourself