Web3 Smart Contract Testing
Master comprehensive testing strategies for smart contracts using Hardhat, Foundry, and advanced testing patterns.
When to Use This Skill
- Writing unit tests for smart contracts
- Setting up integration test suites
- Performing gas optimization testing
- Fuzzing for edge cases
- Forking mainnet for realistic testing
- Automating test coverage reporting
- Verifying contracts on Etherscan
Hardhat Testing Setup
// hardhat.config.js
require("@nomicfoundation/hardhat-toolbox");
require("@nomiclabs/hardhat-etherscan");
require("hardhat-gas-reporter");
require("solidity-coverage");
module.exports = {
solidity: {
version: "0.8.19",
settings: {
optimizer: {
enabled: true,
runs: 200,
},
},
},
networks: {
hardhat: {
forking: {
url: process.env.MAINNET_RPC_URL,
blockNumber: 15000000,
},
},
goerli: {
url: process.env.GOERLI_RPC_URL,
accounts: [process.env.PRIVATE_KEY],
},
},
gasReporter: {
enabled: true,
currency: "USD",
coinmarketcap: process.env.COINMARKETCAP_API_KEY,
},
etherscan: {
apiKey: process.env.ETHERSCAN_API_KEY,
},
};Unit Testing Patterns
const { expect } = require("chai");
const { ethers } = require("hardhat");
const {
loadFixture,
time,
} = require("@nomicfoundation/hardhat-network-helpers");
describe("Token Contract", function () {
// Fixture for test setup
async function deployTokenFixture() {
const [owner, addr1, addr2] = await ethers.getSigners();
const Token = await ethers.getContractFactory("Token");
const token = await Token.deploy();
return { token, owner, addr1, addr2 };
}
describe("Deployment", function () {
it("Should set the right owner", async function () {
const { token, owner } = await loadFixture(deployTokenFixture);
expect(await token.owner()).to.equal(owner.address);
});
it("Should assign total supply to owner", async function () {
const { token, owner } = await loadFixture(deployTokenFixture);
const ownerBalance = await token.balanceOf(owner.address);
expect(await token.totalSupply()).to.equal(ownerBalance);
});
});
describe("Transactions", function () {
it("Should transfer tokens between accounts", async function () {
const { token, owner, addr1 } = await loadFixture(deployTokenFixture);
await expect(token.transfer(addr1.address, 50)).to.changeTokenBalances(
token,
[owner, addr1],
[-50, 50],
);
});
it("Should fail if sender doesn't have enough tokens", async function () {
const { token, addr1 } = await loadFixture(deployTokenFixture);
const initialBalance = await token.balanceOf(addr1.address);
await expect(
token.connect(addr1).transfer(owner.address, 1),
).to.be.revertedWith("Insufficient balance");
});
it("Should emit Transfer event", async function () {
const { token, owner, addr1 } = await loadFixture(deployTokenFixture);
await expect(token.transfer(addr1.address, 50))
.to.emit(token, "Transfer")
.withArgs(owner.address, addr1.address, 50);
});
});
describe("Time-based tests", function () {
it("Should handle time-locked operations", async function () {
const { token } = await loadFixture(deployTokenFixture);
// Increase time by 1 day
await time.increase(86400);
// Test time-dependent functionality
});
});
describe("Gas optimization", function () {
it("Should use gas efficiently", async function () {
const { token } = await loadFixture(deployTokenFixture);
const tx = await token.transfer(addr1.address, 100);
const receipt = await tx.wait();
expect(receipt.gasUsed).to.be.lessThan(50000);
});
});
});Foundry Testing (Forge)
// SPDX-License-Identifier: MIT
pragma solidity ^0.8.0;
import "forge-std/Test.sol";
import "../src/Token.sol";
contract TokenTest is Test {
Token token;
address owner = address(1);
address user1 = address(2);
address user2 = address(3);
function setUp() public {
vm.prank(owner);
token = new Token();
}
function testInitialSupply() public {
assertEq(token.totalSupply(), 1000000 * 10**18);
}
function testTransfer() public {
vm.prank(owner);
token.transfer(user1, 100);
assertEq(token.balanceOf(user1), 100);
assertEq(token.balanceOf(owner), token.totalSupply() - 100);
}
function testFailTransferInsufficientBalance() public {
vm.prank(user1);
token.transfer(user2, 100); // Should fail
}
function testCannotTransferToZeroAddress() public {
vm.prank(owner);
vm.expectRevert("Invalid recipient");
token.transfer(address(0), 100);
}
// Fuzzing test
function testFuzzTransfer(uint256 amount) public {
vm.assume(amount > 0 && amount <= token.totalSupply());
vm.prank(owner);
token.transfer(user1, amount);
assertEq(token.balanceOf(user1), amount);
}
// Test with cheatcodes
function testDealAndPrank() public {
// Give ETH to address
vm.deal(user1, 10 ether);
// Impersonate address
vm.prank(user1);
// Test functionality
assertEq(user1.balance, 10 ether);
}
// Mainnet fork test
function testForkMainnet() public {
vm.createSelectFork("https://eth-mainnet.alchemyapi.io/v2/...");
// Interact with mainnet contracts
address dai = 0x6B175474E89094C44Da98b954EedeAC495271d0F;
assertEq(IERC20(dai).symbol(), "DAI");
}
}Advanced Testing Patterns
Snapshot and Revert
describe("Complex State Changes", function () {
let snapshotId;
beforeEach(async function () {
snapshotId = await network.provider.send("evm_snapshot");
});
afterEach(async function () {
await network.provider.send("evm_revert", [snapshotId]);
});
it("Test 1", async function () {
// Make state changes
});
it("Test 2", async function () {
// State reverted, clean slate
});
});Mainnet Forking
describe("Mainnet Fork Tests", function () {
let uniswapRouter, dai, usdc;
before(async function () {
await network.provider.request({
method: "hardhat_reset",
params: [
{
forking: {
jsonRpcUrl: process.env.MAINNET_RPC_URL,
blockNumber: 15000000,
},
},
],
});
// Connect to existing mainnet contracts
uniswapRouter = await ethers.getContractAt(
"IUniswapV2Router",
"0x7a250d5630B4cF539739dF2C5dAcb4c659F2488D",
);
dai = await ethers.getContractAt(
"IERC20",
"0x6B175474E89094C44Da98b954EedeAC495271d0F",
);
});
it("Should swap on Uniswap", async function () {
// Test with real Uniswap contracts
});
});Impersonating Accounts
it("Should impersonate whale account", async function () {
const whaleAddress = "0x...";
await network.provider.request({
method: "hardhat_impersonateAccount",
params: [whaleAddress],
});
const whale = await ethers.getSigner(whaleAddress);
// Use whale's tokens
await dai
.connect(whale)
.transfer(addr1.address, ethers.utils.parseEther("1000"));
});Gas Optimization Testing
const { expect } = require("chai");
describe("Gas Optimization", function () {
it("Compare gas usage between implementations", async function () {
const Implementation1 =
await ethers.getContractFactory("OptimizedContract");
const Implementation2 = await ethers.getContractFactory(
"UnoptimizedContract",
);
const contract1 = await Implementation1.deploy();
const contract2 = await Implementation2.deploy();
const tx1 = await contract1.doSomething();
const receipt1 = await tx1.wait();
const tx2 = await contract2.doSomething();
const receipt2 = await tx2.wait();
console.log("Optimized gas:", receipt1.gasUsed.toString());
console.log("Unoptimized gas:", receipt2.gasUsed.toString());
expect(receipt1.gasUsed).to.be.lessThan(receipt2.gasUsed);
});
});Coverage Reporting
# Generate coverage report
npx hardhat coverage
# Output shows:
# File | % Stmts | % Branch | % Funcs | % Lines |
# -------------------|---------|----------|---------|---------|
# contracts/Token.sol | 100 | 90 | 100 | 95 |Contract Verification
// Verify on Etherscan
await hre.run("verify:verify", {
address: contractAddress,
constructorArguments: [arg1, arg2],
});# Or via CLI
npx hardhat verify --network mainnet CONTRACT_ADDRESS "Constructor arg1" "arg2"CI/CD Integration
# .github/workflows/test.yml
name: Tests
on: [push, pull_request]
jobs:
test:
runs-on: ubuntu-latest
steps:
- uses: actions/checkout@v2
- uses: actions/setup-node@v2
with:
node-version: "16"
- run: npm install
- run: npx hardhat compile
- run: npx hardhat test
- run: npx hardhat coverage
- name: Upload coverage to Codecov
uses: codecov/codecov-action@v2