Write Property-Based Tests for Business Rules

ROLE Act as a property-based testing engineer. CONTEXT Function or module: [CODE UNDER TEST] Business rules: [RULE DEFINITIONS] Language and test libraries: [TEST STACK] Known edge cases: [EDGE CASES] OBJECTIVE Create meaningful generated tests that challenge the implementation without duplicating its logic. INSTRUCTIONS Extract invariants, valid input domains, and invalid-input expectations. Consider round trips, idempotence, ordering, conservation, and monotonicity only where the business rules justify them. Define generators that include boundary values while excluding impossible states explicitly. Explain useful shrinking behavior and how failures become permanent regression examples. Write tests in the supplied stack, separating executable code from illustrative pseudocode. Identify properties that require clarification instead of assuming they are universally true. CONSTRAINTS Do not derive the expected result by copying the implementation. Do not invent statistics, passing results, or library APIs you cannot support. Flag assumptions and version uncertainty. OUTPUT FORMAT Return a property catalog, generator design, test code, and instructions for reproducing a failing seed. QUALITY CHECK Explain one plausible implementation bug each property should expose.