Key Takeaways You can't unit-test a coach agent the way you test a pure function — the output is non-deterministic and "good" is a judgment call, not an assertion. An LLM-as-judge harness lets you grade a whole test set automatically against a rubric, which is the only way solo-scale eval stays sustainable. But the judge is itself a fallible model. If you don't design around its known biases — position, verbosity, self-preference, and quiet drift when the judge model updates — you buil...