An agent patch is a hypothesis. A test suite is the only evidence a reviewer gets. Most suites fail at that job in three reproducible ways: assertions the agent can reverse-engineer, fixtures that regenerate and drift, and flaky tests that flap between green and red without a single commit. This article is a three-layer contract that closes all three: property checks for invariants, hash-pinned fixtures for determinism, and a flake quarantine that runs before the agent ever sees the suite.
The evidence problem
assert(add(2, 2) == 4) is not evidence. It is a target. An agent that watches that failure can patch until the value matches, and the suite turns green even when the surrounding logic is wrong. More assertions do not fix this; they add more targets.
Tests only become evidence when the agent cannot predict what will be checked. That requires three changes at once.
Layer 1: Property checks turn values into relationships
