Write and debug Foundry tests and Solidity scripts. Use when writing unit, fuzz, fork, or invariant tests, writing bulloak BTT .tree specs (Branching Tree Technique), using cheatcodes, benchmarking gas, measuring coverage, writing deploy scripts, or working in tests/ or script/.
Write and modify production Solidity contracts in Foundry projects. Use when writing a contract, implementing a function, adding errors, events, or structs, designing contract architecture, optimizing gas, hardening security, planning upgrades, or working in src/.