Test design can be compared with the design of buildings and other structures in architecture. Both activities require the development of detailed plans and blueprints that generate the actual buildings or test forms. When the blueprints are created, architects know what to what use the building is going to be put. Without knowledge of purpose they simply would not be able to design a building. Similarly, test designers need to know what inferences we intend to make from scores, and what decisions are to be made on the basis of those scores. Tests without purpose generate validity chaos. Similarly, when buildings change their use, architects must retrofit the building and follow standard procedures to ensure that health and safety regulations are being met, and that the proposed changes make the building fit for its new users. We argue that test designers must follow similar principles if the purpose of a test is to be changed or extended, or used on a group of test takers for whom it was not originally intended. We term this process test retrofit, and use the example of immigration testing to illustrate the argument.