testing

Invariant testing in Foundry verifies that core economic invariants hold across arbitrary state changes. You define invariant assertions and the fuzzer generates sequences of function calls to find edge cases that break protocol logic.

Fork testing is the best way to verify external protocol integrations. Foundry fork tests simulate live network conditions, allowing you to test interactions with existing protocols like Uniswap against actual chain state.

Fuzz tests work by automatically generating random inputs for function parameters. Foundry repeatedly executes the test with varied data to uncover overflow, rounding, or edge case vulnerabilities in mathematical operations.

Common pitfalls include over-testing internal implementation details rather than external behavior and relying solely on unit tests. You should focus on edge cases, economic invariants, and integration behavior to ensure robustness.

You need fork testing when your DeFi protocol interacts with external contracts. Standard unit tests isolate logic, while fork tests validate integration with live network state and external protocol dependencies.

Foundry handles both unit and advanced testing strategies natively. It supports basic unit tests for core logic alongside fuzz, fork, and invariant testing methodologies to ensure comprehensive smart contract security.