I am not quite sure, but I think the school can make passing the hesi test a requirement. If your school had low NCLEX passing rates in the past, they use the hesi test as an indicator of who may fail. The school doesn't want those at risk of failing the NCLEX to take the exam because it ruins the school's passing percentage...and the school can be put on probation...and eventually lose their accredidation (sp?).
The school I went to made passing the hesi test a requirement the year after I graduated. The students a year under me are required to pass hesi before they can get their slips of paper saying they can sit for NCLEX...and this wasn't a requirement when they signed up for the program.
My class took the hesi test as a trial run. I don't really think the hesi test was like NCLEX. The hesi was very factual...and NCLEX was almost all critical thinking and prioritizing.
The hesi test can be a positive thing. It can give you the confidence that if you pass it...then you will pass NCLEX. I don't think we had anyone in the class that passed hesi, but failed NCLEX. Students typically do better on NCLEX than on the hesi. Also, the hesi tests can show you your weak areas that you will need to work on.
Don't worry...you'll be fine.