Our best advice for those studying for a promotional exam that includes an assessment center component, which may or may not include a simulation, but most likely will, keep in mind that the assessors/raters are really looking to spot those who really have demonstrated those skills they post on the job descriptions... by noticing how they utilize those core job dimensions by their actions/words.
While the typical company officer handles many routine issues, the bulk of a rating system for a promotional generally hopes to identify key behaviors in either some form of counseling/disciplinary setting with a subordinate, managing a meeting, (usually with a "new" unit) or a "community meeting," coupled with some form of a presentation. In addition, the venerable "in-basket" is very common and is getting pretty high tech as more agencies use computers with an internal email system to communicate vs. the "old" handwritten memo's or responses to in-basket items. Consequently, the more comfortable you are in these types of "real" scenarios, the more likely you are to be more confident and competent to any raters. As someone once said to me, "Practice may not make you perfect, but it will make you "better!"