School says class 3 children move to the main block 'after an assessment'. Formality, or a real test?

Is this something to prepare her for, or just a formality? Our daughter is finishing class 2. The school has a separate junior block, and the circular says children moving up to class 3 in the main block will have a 'short assessment' later this month. No syllabus, no details, nothing else. She's doing fine in class, but she panicked when she heard the word. If your child's school does something like this, what was it really like?