Test my fault coverage

Understanding fault coverage vs. test coverage in Design for Testability

This is a medium-difficulty question on Design for Testability (DFT) that probes the distinction between two fundamental metrics used to evaluate the quality and completeness of digital test suites. It's the kind of question that appears in hardware design interviews and qualification rounds where rigorous testing methodology matters.

Test coverage and fault coverage are related but distinct concepts. Test coverage typically measures which elements of the design (nodes, transitions, conditions) are exercised by a test pattern set, while fault coverage measures what proportion of possible manufacturing defects—modeled as stuck-at faults, delay faults, or other failure modes—can actually be detected by those same patterns. A test pattern may achieve high node coverage without detecting all realistic fault types, making this distinction essential for assessing whether a test suite is truly adequate.

• Stuck-at-zero and stuck-at-one fault models
• Controllability and observability in test design
• Relationship between code coverage and defect detection