3 · Fuzzing & Invariant Testing

3. Property-Based Fuzzing with Foundry & Echidna

Stateless vs stateful fuzzing, defining system invariants, and breaking assertions.

11 min read · 2 MCQs

Invariant Testing Methodology

Unit tests only test scenarios the developer anticipated. Invariant fuzz testing defines core mathematical truths that must NEVER break (e.g. `totalVaultAssets >= totalSharesMinted`), and automatically bombards the protocol with millions of randomized transaction combinations to find breaking execution paths.

Stateful vs Stateless Fuzzing

Stateless fuzzing tests a function with randomized inputs in isolation. Stateful fuzzing executes sequences of multiple transactions across different accounts in succession, discovering complex vulnerabilities that emerge only after a specific state history.

Chapter quiz

2 questions · pass mark 75%

1. What is a system invariant in smart contract testing?
2. How does stateful fuzzing find bugs that unit tests miss?