There isn't a lot that I do to "Set the Stage" on test days, other than to make sure that my students are fully aware of what they will be assessed on, what tools they can use, and whether the assessment will be individual or group. In addition, my students know what to expect in the classroom in terms of seating, test distribution and collection, and what to do if they finish early (see my strategies folder) I've included a video narrative with this section explaining a bit about how I decide what type of assessment to give when.
You will want to have copies of the Stats Assessment as well as any reference sheets you will be allowing your students to use. I always have a Chi-square table available for those who want one. While my students are testing, I walk around monitoring their progress and clarifying as needed. This walkabout gives me insight into which problems are stumping my students even before I begin grading their papers and also gives me an overview of how they're approaching each problem so I can begin to plan which math practices to reinforce in my next unit.
As my students complete the assessment, they turn it in along with any additional work they want me to consider. I tell them in advance that if they are working on additional paper(s) I will only review those problems that are appropriately labeled...this sounds like I'm being picky, but I've found that this simple requirement not only helps me, but also helps my students stay organized as they work through the problems. I've written an Answer Guide which includes some of my reasoning for selecting the four problems I did for the assessment.