Fault coverage

If at least one of the outputs differs from what is to be expected, the fault is said to be detected.

Conceptually, the total number of simulation runs is twice the number of pins (since each pin is stuck in one of two ways, and both faults should be detected).

First, the designer can augment or otherwise improve the vector set, perhaps by using a more effective automatic test pattern generation tool.

Second, the circuit may be re-defined for better fault detectability (improved controllability and observability).

Third, the designer may simply accept the lower coverage.