web3-testing

Use Hardhat with Chai and ethers.js to write unit tests organized in describe blocks. Load deployment fixtures with loadFixture, assert state changes with expect, and test events, reverts, and token balance changes.

Write a Forge test function prefixed with testFuzz that accepts random input parameters. Use vm.assume to constrain inputs to valid ranges, then assert invariants like balance correctness after transfers.

Hardhat uses JavaScript with Chai and ethers.js, suiting teams already in the Node.js ecosystem. Foundry writes tests in Solidity itself with cheatcodes like vm.prank and vm.deal, offering faster execution and native fuzzing.

Use mainnet forking by configuring a fork URL and block number in hardhat.config.js or calling vm.createSelectFork in Foundry. This lets tests interact with live contracts like Uniswap and DAI at a pinned block.

Impersonation requires calling hardhat_impersonateAccount through the network provider before getting the signer. The impersonated account also needs ETH for gas, which you can set with hardhat_setBalance or vm.deal.

Enable hardhat-gas-reporter in the config to log gas per function call, or capture receipt.gasUsed after awaiting a transaction. Compare gasUsed values between contract implementations to verify optimizations.