1)I have been to several interviews and it was 50/50 change to be tested. In a couple of interviews I had a written test and some a had hands on.
In the written test I had question such as: What is the 5 elements required for a map? Name 3 ESRI Extensions? What type of license does ESRI offer?
For the hands on they requested that I bring in a couple of layers. (They did provide the location). They requested that I started editing the layer? Change the coordinate system? Tell them how many features where in that layer? Change colors! Pretty much it was very beginner type of questions.
My recommendation to you is to get yourself confortable with the basics. Learn the basic terminology. Try to figure out what software they are using prior to the interview, and learn a little bit about.
GIS field is a very broad, and employers are aware of that. Just remind them you are willing to learn if you don't know the subject.
I hope this help out! Good luck!