Just some advice for anyone who happens upon this post: STUDY. The ONCC website is quite helpful with information that will help you prepare. Follow the OCN blueprint as a study guide. The site also explains how the test is graded, with several versions of the test. It's possible to receive a difficult test that allows you to get more questions wrong and still pass, and vice versa. I have 11 years of oncology experience and studied for a month before taking the exam, and I felt it was tough. I'm guessing my version was one of the hard ones. I used the ONS Core Curriculum for Oncology Nursing study guide and the companion test question book (the questions in the book are significantly more complex than the actual test questions, but it's a great way to learn the content). I also purchased the test bundle on the ONCC website, plus the free test. Doing so gives you 200 questions to practice with that accurately reflect the test questions. There won't be any of the same questions on the test, but the style and material are there. I do not recommend any other study guides, the question styles are incorrect, and I found some errors in the content, especially the Mometrix guides.
Regardless of how long you have been in oncology, this is not a test you can walk into and take. The more experience you have, the easier it will be, but you still need to study. I felt confident with about 40% of the test questions based on experience alone, but the test covers so much content that it's impossible to know everything only from experience.
Once you complete the test, you determine if you pass or fail immediately. You are given a score breakdown to determine areas that require additional ILNA points. To renew certification every four years, everyone must complete a minimum of 25 ILNA points, plus any additional in the areas that need further studying. Thankfully my studying paid off, as I didn't have to complete any additional points.
I hope this helps anyone reading, and best of luck!