Glossary comparison
Fault coverage vs Test coverage: what is the difference?
The difference
Test coverage removes untestable faults from the denominator, so it measures coverage of the logic that can be tested. Fault coverage keeps them in and is the stricter figure.
Fault coverage keeps untestable faults in the denominator, so it is lower. Some engineers prefer it as the stricter quality measure, since any defect can matter, while test coverage shows how well the patterns did on faults they could catch.
The two terms
Fault coverage
The fraction of faults in the fault list that a pattern set detects, counting only faults that are actually detected in the numerator and every fault including untestable ones in the denominator.
Test coverage
The fraction of testable faults detected, excluding faults proven undetectable by design from the denominator. It is the number usually quoted in signoff because it reflects how well the pattern set did on the faults it could have caught.
Side by side
| Field | Fault coverage | Test coverage |
|---|---|---|
| Stands for | Not an abbreviation | Not an abbreviation |
| Type | Metric | Metric |
| Domain | Test & DFT | Test & DFT |
| Group | ATPG and fault models | ATPG and fault models |