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Fuzz Testing

1 min read
Pronunciation
[fuhz tes-ting]
Analogy
Like stress‑testing a bridge by driving vehicles of varying weights and sizes across it to find structural weaknesses.
Definition
An automated software testing technique that feeds random or malformed inputs into smart contracts or applications to uncover crashes, assertion failures, or unexpected behavior.
Key Points Intro
Fuzz testing uncovers edge‑case bugs by bombarding code with diverse inputs.
Key Points

Input generation: Creates random, boundary, or mutated data.

Instrumentation: Monitors execution for exceptions or gas spikes.

Coverage-guided: Adjusts inputs to explore untested branches.

Automated harness: Runs continuous fuzz campaigns in CI.

Example
Echidna fuzzer generates random sequences of contract calls on a DeFi protocol and reports any invariant violations or reverts.
Technical Deep Dive
Fuzzer integrates with EVM test framework, instruments bytecode to track branch coverage, and uses genetic algorithms to evolve input seeds. Detected failures are minimized to reproducible test cases.
Security Warning
Fuzz testing may miss logic flaws requiring specific state setups; combine with manual review.
Caveat
Random testing can be resource-intensive; focus on critical modules.
Related Terms
Static Analysis
Symbolic Execution

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