Cognitive psychology principles have been heralded as possibly central to construct validity. In this paper, testing practices are examined in three stages: (a) the past, in which the traditional testing research paradigm left little role for cognitive psychology principles, (b) the present, in which testing research is enhanced by cognitive psychology principles, and (c) the future, for which we predict that cognitive psychology's potential will be fully realized through item design. An extended example of item design by cognitive theory is given to illustrate the principles. A spatial ability test that consists of an object assembly task highlights how cognitive design principles can lead to item generation.