Just like buildings, tests are designed and built for specific purposes, people, and uses. However, both buildings and tests grow and change over time as the needs of their users change. Sometimes, they are also both used for purposes other than those intended in the original designs. This paper explores architecture as a metaphor for language test development. Firstly, it describes test purpose and use, and how this affects test design. Secondly, it describes and illustrates the layers of test architecture and design. Thirdly, it discusses the concept of test retrofit, which is the process of altering the test after it has been put into operational use. We argue that there are two types of test retrofit: an upgrade and a change. Each type of retrofit implies changes to layers of the test architecture which must be articulated for a validity argument to be constructed and evaluated. As is true in architecture, we argue that a failure to be explicit about retrofit seriously limits validity claims and clouds issues surrounding the intended effect of the test upon users. (Contains 2 footnotes, 1 table, and 5 figures.)