While asynchronous circuits offer potential advantages over synchronous circuits, particularly in the form of low power and low noise properties, it is widely held that they are more difficult to test. The self-checking properties of semi-modular asynchronous circuits with respect to certain stuck-at faults have been known for many years, but the restrictions have been such that it has not been feasible to make use of this property to enhance testability. In this paper we demonstrate the feasibility of a technique to determine whether a proposed asynchronous circuit implementation is totally self-checking with respect to all output stuck-at-faults. This test can he incorporated into the design process to select a self-checking implementation when several alternatives are available.