# Mvx Property Testing

> Using fuzz tests in Rust for invariants. Use when this capability is needed.

- Skill: `tomevault-io/mvx-property-testing` (Agent Skill, multi-file: 2 files)
- Install (CLI): `npx skillmds@latest add tomevault-io/mvx-property-testing`
- Raw SKILL.md: https://api.skillmd.com/api/skills/tomevault-io/mvx-property-testing/raw
- Safety review: pending
- Works with: Claude Code, Claude.ai, OpenAI Codex
- Category: Coding & Dev Tools
- Author: tomevault-io (https://skillmd.com/u/tomevault-io)
- Updated: 2026-09-17
- Page: https://skillmd.com/skills/tomevault-io/mvx-property-testing

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# MultiversX Property Testing

This skill guides you in using property-based testing (fuzzing) to find edge cases in Smart Contract logic.

## 1. Tools
- **`cargo fuzz`**: Standard Rust fuzzer.
- **`proptest`**: Property testing framework for Rust.

## 2. Methodology
Defining Invariants:
- "Total Supply MUST equal sum of all balances."
- "User balance MUST NOT decrease if deposit fails."

## 3. Implementation (RustVM)
Write a test that:
1.  Takes random input (random amounts, random user IDs).
2.  Executes the contract logic via `blockchain_mock`.
3.  Asserts the invariant holds.

## 4. Example
```rust
proptest! {
    #[test]
    fn test_deposit_always_increases_balance(amount in 0u64..1_000_000u64) {
        let mut setup = Setup::new();
        setup.deposit(amount);
        assert_eq!(setup.balance(), amount);
    }
}
```

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<!-- tomevault:4.0:skill_md:2026-04-11 -->