Property Based Testing

Express a domain invariant independently of the implementation before writing generators.

Decisions

• Generate valid and deliberately invalid inputs; preserve domain constraints instead of filtering nearly everything.
• Use round-trip, conservation, monotonicity, ordering, or reference-model properties where justified.
• Keep failure seeds and minimized examples for regression reproduction.

Acceptance

Show that a known faulty implementation or mutation fails the property. Report execution budget, seed, smallest failing input, and any untested domain.