I think it depends on 1. which test you are taking 2. where is your experience and 3. what materials are you using.
Take me, for example - I took the FNP test after going through an FNP program with a background in psych. I also used a test prep book that did not simulate the questions correctly. I did not pass 1st time (it was close!) but after getting a book that was a better match to the test, I sailed through.
Then, when taking the Psych. NP test, althought I studied I don't think it helped much. Most of the questions I was able to answer based on my experience alone!! Did very well.