I took 2 months for preparation and 4 years of experience in Hibernate.
Enthusware test were very helpful, they mostly matches with real time exam, in mock exam I scored 85-89% and I scored same number in real exam.
Here are my tips:
1) Read pro JPA and JPA related notes from java.boot.by
2) Give Enthuware test topic vise, you will have to create your custom test cases.
3) Note down points where you made mistake, read explanation from Enthusware.
4) Again read JPA book and give all 4 Enthusware test. My score for Enthusware tests was 85-89%
5) You have to read PRO JPA book because question are asked from all the topics in book.