Noncheckpoint target faults-how to order them?

M. Abramovici, P.R. Menon, and D.T. Miller (see IEEE Trans. on Computers, vol.C-35, no.8, p.760-71, Aug. 1986) observed that the checkpoint faults are not sufficient target faults for test generation in combinational circuits and presented an algorithm to select the additional target faults so as to ensure sufficiency. A critical review of their algorithm is presented, and certain disadvantages of that algorithm are brought to light. A revised algorithm incorporating an additional stage of fault simulation and judicious selection of noncheckpoint target faults based on a probabilistic model is developed. The concepts of cover forest and benefit indicators are developed and used effectively in guiding the judicious selection of noncheckpoint target faults, thus minimizing the total number of calls made to the test generation routine