Fusion nuclear technology testing issues are reviewed, covering the technical disciplines of materials science, structural mechanics, MHD, thermal hydraulics, tritium recovery, and others. These issues represent the largest uncertainties whose resolution will require new knowledge through experiments, models, and theory in order to demonstrate the feasibility and attractiveness of the entire fusion nuclear system. Needed tests range in complexity, including basic materials property data, exploration of individual and interactive phenomena, and fully integrated tests. By addressing the complete array of testing issues, this work helps to define needed engineering research which should prove useful in future fusion program planning.