Agent Series (21): Harness Testing — 45 Tests, How They're Designed, and What Bugs They Found (opens in new tab)

Why a Harness Needs Its Own Test Suite Ordinary business logic tests cover "what should happen." Harness tests also cover what must NOT happen: Unregistered actions cannot execute IRREVERSIBLE actions cannot run before approval Once budget is exhausted, every action must be blocked Injection payloads must be detected Negative tests like these don't emerge naturally from business test frameworks. A dedicated Harness test suite treats them as first-class citizens. Suite Structure tests/ ├── con...