You do not get the test done by a vet. You have to order the kit from the OFA website, https://secure.offa.org/cart.html It costs $65.
Please keep in mind this is only 1 of the hereditary diseases in basenjis and that the others do not have DNA tests so the only way to estimate the risk of producing the disease is through testing not only your animal but also have the test results of parents, grandparents, siblings, aunts and uncles.
The Basenji Club of America recommends at a minimum breeders test their breeding stock for Fanconi, Hip Dysplasia (done after 2 years of age), Hypothyroidism (OFA recommends to be done every year until 5 years of age then every other year), and a CERF exam to check for heritable eye disorders (CERF is only good for one year and must be repeated).
There is much more to breeding than just have a dog that looks like a basenji. In addition to health concerns, conformation is much more than that and cannot be judged from the casual shots usually shared on a forum like this and really is something best assessed in person where the evaluator can feel the underlying structure of the dog.