A must-pass case is a specific input paired with what the product must always get right - binary pass/fail. Build the list from Analyze: each top failure becomes a case that catches it.

Cases come in two kinds: rule-checkable (contains X, avoids Y) vs judgment (tone, faithfulness). Knowing which tells you how to check - and what to ask eng to automate later.

A checklist you write once and forget is useless. Re-run it every time you change the product. Start with a handful covering top failures; grow as you find new ones. Those cases are your goldens - ground truth for what good looks like.