All tests pass. The deploy goes green. But your LLM feature degrades silently in production — and your test suite never noticed. Here's the fundamental reason why, and what actually works instead. Picture this: you've built a feature that uses an LLM to classify customer support tickets. You wrote unit tests. You wrote integration tests. They all pass on every CI run. You deploy with confidence. Three weeks later, a customer flags that the routing has been wrong for days. You check your test suite — it's green. You check the model configuration — nothing changed on your end. But something changed. And your entire testing infrastructure missed it completely. This isn't a gap in your test coverage. It's a fundamental mismatch between how software testing works and how LLMs behave. What Unit Tests Are Built For Unit tests work because the systems they test are deterministic . Given input X, a pure function always returns output Y. The test captures that contract. If someone breaks it, the test fails.…