I just posted this in another thread, but it applies to to your question to. Hope it helps.
The "casting call" is how I went through my formal interview. In my case, you could bring a model, but you didn't have to. I didn't bring a model, so they paired me up with another applicant and we did each others makeup.
They provided makeup, brushes and gave us 5 or 6 completed face charts to chose a look from. I picked a look and did that on my model. One thing to keep in mind is that the face charts may or may not list the colours they used and even if it does list colours, it doesn't necessarily mean you will have those colours to work with. The look may be your interpretation of the face chart look using different colours.
They will also time the application. They are very big on this. Wear a watch if you need to and plan out how much time you want to spend on each area of the face.
Be friendly and talkative about the process with your model, but don't let it distract you and lose track of time.
Also be mindful of sanitation issues. They will keep an eye on that.
After the makeup application portion, there was a verbal interview. I guess they want to see if you have the chops before they waste time talking to you.
I wore all black. The interview isn't the time to push the envelope. Definitely be trendy/fashion forward. The gals who didn't wear all black and "look the part"...well, to be honest, I never saw them after the casting call.
Don't necessarily expect them to move fast on hiring you or working with your paperwork. Don't get nervous if you don't hear from them right away. Some people wiz right through the process, but others get caught up in the Estee Lauder "machine" and it takes forever.
That was my experience. I would highly recommend that you contact the person who scheduled the interview with you and ask them your questions. Each area might do things just a bit differently and being mentally prepared will give you an edge.
Hope that helped.
Well, that's about it. I hope it goes well for you. Good luck! Let us know how it goes.