---

name: web3-testing description: Test smart contracts comprehensively using Hardhat and Foundry with unit tests, integration tests, and mainnet forking. Use when testing Solidity contracts, setting up blockchain test suites, or validating DeFi protocols.

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

Resources

• references/hardhat-setup.md: Hardhat configuration guide
• references/foundry-setup.md: Foundry testing framework
• references/test-patterns.md: Testing best practices
• references/mainnet-forking.md: Fork testing strategies
• references/contract-verification.md: Etherscan verification
• assets/hardhat-config.js: Complete Hardhat configuration
• assets/test-suite.js: Comprehensive test examples
• assets/foundry.toml: Foundry configuration
• scripts/test-contract.sh: Automated testing script

Best Practices

1. Test Coverage: Aim for >90% coverage
2. Edge Cases: Test boundary conditions
3. Gas Limits: Verify functions don't hit block gas limit
4. Reentrancy: Test for reentrancy vulnerabilities
5. Access Control: Test unauthorized access attempts
6. Events: Verify event emissions
7. Fixtures: Use fixtures to avoid code duplication
8. Mainnet Fork: Test with real contracts
9. Fuzzing: Use property-based testing
10. CI/CD: Automate testing on every commit