I got my 107, due again this winter to renew. I used the study guide from here: https://www.kingschools.com/ground-school/drone-pilot/ to prep for the test. You are allowed to retake the test if you fail, but it costs each time you take the test. So the study guide is worth the money in my opinion. A current pilot may pass the 107 test without additional study, but I'd recommend studying for the test.