Move Beyond String Matching: Reliable Testing for Non-Deterministic Systems

AI agent testing with equality assertions creates flaky CI pipelines because LLM outputs are inherently non-deterministic—same prompt, same model, same temperature can produce different tokens. Testing invariants instead of strings provides a deterministic, reliable alternative: verify properties that must be true (like containing actual customer IDs, proper length, no system prompt leaks) regardless of wording. This transforms agent testing from an impossible task into a practical, solvable problem.