Automation for product development and manufacturing is changing to take advantage of the recent expansion of the Internet and the computing technologies supporting it. These processes are becoming more software independent, and the software used is becoming more modularized, allowing for the creation of customized systems consisting in large part of pre-existing components distributed across a network. This combination of factors leads to considerable flexibility for manufacturing systems, but not without a cost. The reliability of those systems is uncertain given the lack of experience in how to test such systems. To address this need, the National Institute of Standards and Technology''s Manufacturing Systems Integration Division has undertaken a study of how to test interaction-driven manufacturing systems. This paper presents the results of a study of the problems involved in testing these new systems, reports on factors which influence the testability of the systems, and outlines approaches to testing.