Why can't you just use normal unit-test assertions (`assertEquals`) to test LLM output quality?

LLM output is non-deterministic and phrased differently each time even when factually correct, so exact string matching almost always fails even for a 'correct' answer. Evaluators instead use techniques like using a second LLM call to judge whether the output meets criteria (relevance, factual grounding, absence of the actual answer inside the prompt/leakage), producing a score rather than a pass/fail on exact text.