Random testability of redundant circuits

It is shown that the common belief that any optimized, i.e., nonredundant, circuit is easier to test than its nonoptimized counterpart is not fully justified. It is demonstrated by example that a redundant circuit may be more suitable for random testing than its optimized counterpart. A rule which specifies when redundancy is likely to enhance random testability of a two-level AND-OR gate network is formulated.>