The first time around I would not put too much money into it unless you are going to attend classes in a classroom setting. And there is a much higher probability that you may need to retest if:
1) You aren’t a good test taker/student. If you struggled in school, you may need to work on how you study a bit first. I teach prep courses for the certification exams. And the first thing I ask a potential student is, how were your grades in high school/college in science classes? If they tell me they didn’t do so well, they are good candidates for my courses. I actually discourage good students from taking my courses unless they need help with the practical application.
If you aren’t that good of a student, I would recommend you buy the book/study materials and really read through the material carefully a few times over. I buy various textbooks just to read them for myself and read them at least two times through cover to cover. If the material is highly technical or advanced, I read the textbooks until I completely understand the material. I do the same with CECs that I take. And take notes in your own words as to what the material is about on each topic.
2) If you are not a good test taker. If you are not a good test taker, I recommend you do as many practice tests as you can. Taking tests is just like anything else, the more you do it the better you will be at doing it. When you take a practice test, treat it like it is the real deal. That will give you an idea of how well you do with the format. And when you look at the correct answers, really tear apart the question to try to see why and how the question was framed for that answer.
And try to relax. Yes, retaking the test is a pain and an expense. But people do have to retake cert exams. It isn’t a big deal. Doctors, dentists, and lawyers take their board/bar exams over and still become professionals.