Misuse case testing

Misuse case testing verifies what a system must not allow. Where a use case describes a legitimate actor achieving a goal, a misuse case inverts it: a hostile actor attempting to abuse the same functionality, such as submitting malformed input, replaying a transaction, skipping a payment step, or escalating privileges. Testers derive these abuse scenarios deliberately, then confirm the system rejects each one, failing safely and logging the attempt rather than obliging the attacker.

The subtlety is that positive functional testing cannot find these defects. A system can pass every test proving it does what it should while remaining wide open to things it should never permit, because nobody asked. Misuse cases complement positive testing, never replace it, and they are strongest when derived from threat modeling, which supplies the attacker goals worth inverting. Unlike a full penetration test, misuse case testing is planned into the development and test cycle and targets specified abuse scenarios rather than open-ended attack paths.

Exam relevance: if a scenario mentions testing what the system should not do, inverted use cases, or verifying that invalid and malicious actions are rejected, the answer is misuse case testing. If the scenario involves an authorised team actively exploiting a live environment under rules of engagement, that is penetration testing instead. The tell is placement in the SDLC: misuse case testing is a design-driven verification activity, not an adversarial engagement.