property-based-testing

# Property-Based Testing Guide Use this skill proactively during development when you encounter patterns where PBT provides stronger coverage than example-based tests. ## When to Invoke (Automatic Detection) **Invoke this skill when you detect:** - **Serialization pairs**: `encode`/`decode`, `serialize`/`deserialize`, `toJSON`/`fromJSON`, `pack`/`unpack` - **Parsers**: URL parsing, config parsing, protocol parsing, string-to-structured-data - **Normalization**: `normalize`, `sanitize`, `clean`, `canonicalize`, `format` - **Validators**: `is_valid`, `validate`, `check_*` (especially with normalizers) - **Data structures**: Custom collections with `add`/`remove`/`get` operations - **Mathematical/algorithmic**: Pure functions, sorting, ordering, comparators - **Smart contracts**: Solidity/Vyper contracts, token operations, state invariants, access control **Priority by pattern:** | Pattern | Property | Priority | |---------|----------|----------| | encode/decode pair | Roundtrip | HIGH | | Pure function | Multiple | HIGH | | Validator | Valid after normalize | MEDIUM | | Sorting/ordering | Idempotence + ordering | MEDIUM | | Normalization | Idempotence | MEDIUM | | Builder/factory | Output invariants | LOW | | Smart contract | State invariants | HIGH | ## When NOT to Use Do NOT use this skill for: - Simple CRUD operations without transformation logic - One-off scripts or throwaway code - Code with side effects that cannot be isolated (network calls, database writes) - Te...