Applicants for Fine Art are not required to register for a test. There is no written test.
However, if you are invited to interview in Oxford, there will be a practical test, where you are asked to complete two pieces in a variety of media from a number of possible subjects. You do not need to make any special arrangements for the test, as this will be organised for you by the Ruskin School of Art.
For more information on how to apply for Fine Art, please see the relevant course page.