The impact of fault expansion on the interval estimate for fault detection coverage

A high fault detection coverage is very critical for systems with ultra-safe requirements and fault injection is an effective technique for estimating the coverage. One difficulty of fault injection lies in the huge number of injections that need to be carried out in order to obtain statistically significant results. Fault expansion has been proposed as a means of reducing the number of injections by dividing faults into equivalence classes. We show that this intuitively appealing approach is only effective when each fault equivalence class is a significant portion of the fault population.<>