The development of cost-effective circuits is primarily a matter of economy. To achieve it, design errors and circuit flaws must be eliminated during the design process. To this end, considerable effort must be put into all phases of the design cycle. Effective CAD tools are essential for the production of high-performance digital systems. This thesis describes a CAD tool called LOVERD, which consists of ATPG, fault simulation, design verification and diagnosis. It uses test patterns, developed to detect single stuck-at faults in the gate-level implementation, to compare the results of the functional level description and its gate-level implementation. Whenever an error is detected, the logic diagnosis tool can be used to provide useful information to designers. It is shown that certain types of design errors in combinational logic circuits can be detected and allocated by LOVERD efficiently.