Differential Testing with Foundry
summary
Claims that the Foundry fuzzer plus the ffi cheat code can verify identical behavior between two implementations by running the same fuzzed inputs and comparing rich execution (emits, reverts, storage). Recommends three concrete patterns: a naive single-test comparator, the cport pattern that wraps one test function for both targets (requires VM rollback workarounds), and a preferred pattern that inherits the original test suite and overrides the target factory. Key details: make fuzzing deterministic with a salt and identical dictionary, trade off excluding dictionary entries versus coverage, and a template repo with example tests is provided.
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chapters (6)
- 0:00Introduction
- 3:13Why use differential testing
- 7:10Practical EVM use cases
- 12:34Foundry differential pattern
- 19:12Acknowledgements
- 20:19Q&A
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