Master Web3 Smart Contract Testing

Covers smart-contract testing with Hardhat and Foundry/Forge, from config through CI. Hardhat setup wires @nomicfoundation/hardhat-toolbox, hardhat-etherscan, hardhat-gas-reporter and solidity-coverage, a Solidity 0.8.19 compiler with the optimizer enabled at 200 runs, a hardhat network forking mainnet at a pinned block number, a goerli network, gas-reporter USD pricing via a CoinMarketCap key, and an Etherscan API key for verification. Unit testing patterns use a loadFixture-based deployment fixture, Chai matchers like changeTokenBalances and revertedWith, an emit/withArgs event assertion, hardhat-network-helpers' time.increase() for time-locked logic, and a gas-usage assertion on the transaction receipt.

Foundry/Forge tests use forge-std/Test.sol with vm.prank() to impersonate an address, assertEq assertions on supply and balances, vm.expectRevert() for a rejected zero-address transfer, vm.assume()-bounded fuzz testing over a transfer amount, vm.deal() to fund an address with ETH, and vm.createSelectFork() to fork mainnet and read a real token's symbol().

Advanced patterns cover snapshot-and-revert isolation via evm_snapshot/evm_revert in beforeEach/afterEach, mainnet forking through hardhat_reset pinned to a block and connecting to real Uniswap and DAI contract addresses, impersonating a whale account via hardhat_impersonateAccount to move its tokens in a test, and a side-by-side gas comparison between an optimized and unoptimized contract implementation. Coverage is generated with:

npx hardhat coverage

reporting per-file statement, branch, function and line percentages. Contracts are verified either programmatically via hre.run("verify:verify", {...}) or with npx hardhat verify --network mainnet CONTRACT_ADDRESS "arg1" "arg2". CI/CD integration is a GitHub Actions workflow that installs dependencies, compiles, runs tests and coverage, and uploads results to Codecov.

Ten best practices are called out: aim for over 90% test coverage, test boundary conditions, verify functions don't hit the block gas limit, test for reentrancy vulnerabilities, test unauthorized access attempts, verify event emissions, use fixtures to avoid duplication, test against a real mainnet fork, use property-based fuzz testing, and automate testing in CI/CD on every commit.

Use it for writing unit tests for smart contracts, setting up integration test suites, gas optimization testing, fuzzing for edge cases, forking mainnet for realistic testing, automating coverage reporting, or verifying contracts on Etherscan.

Input is the smart contract or contracts under test. Output is a Hardhat or Foundry test suite, a coverage report, gas-usage comparisons, and, where requested, an Etherscan verification call.

Integrates Hardhat (with hardhat-toolbox, hardhat-etherscan, hardhat-gas-reporter, solidity-coverage), Foundry/Forge, Etherscan verification, mainnet RPC forking, Uniswap and ERC20 mainnet contracts for fork tests, and GitHub Actions plus Codecov for CI. Ships reference guides for Hardhat setup, Foundry setup, test patterns, mainnet forking and contract verification, plus ready assets (assets/hardhat-config.js, assets/test-suite.js, assets/foundry.toml) and scripts/test-contract.sh.

Smart-contract developers writing or hardening a Hardhat or Foundry test suite who need concrete patterns for fixtures, fuzzing, mainnet forking, gas comparison, coverage and Etherscan verification.