2x interviews; 1x test
Chemistry: personal statement & chemistry topic; Biology: described reading & then bio topics
Research on tests; mock interviews
Think out loud - they want to find people that are teachable
Remember this advice isn't official. There is no guarantee it will reflect your experience because university applications can change between years. Check the official Cambridge and Oxford websites for more accurate information on this year's application format and the required tests.
Also, someone else's experience may not reflect your own. Most interviews are more like conversations than tests and like, any conversation, they are quite interactive.
Traveled from Kent, on site-accommodation was offered the night before. Students were on hand to help. First day early morning: supervised classroom
2 interviews with 2 interviewers each. Chemistry: asked about personal statement and worked through an organic synthesis mechanism I have not seen before. It was obviously not a test of knowledge but of thinking.
Biology interview was great fun. They first described who they are what they do, then asked the same about me. This set a very conversational tone. They asked me to describe something I've read recently and had a discussion about that. Next we had a picture round type problem in the general field of evolution. The questions built on each other and was basically a puzzle to work out. Involved topics of natural selection, reproduction, etc.
Read EVERYTHING I could find about the interviews and tests. Tried to answer them all. Had a school
Just be normal, this is not magic. They are normal people looking to see how you do in small group tuition. Take your time, think aloud and be engaging.