Introduction

Foundry, an Ethereum smart contract development framework, offers the capability to run tests across multiple chains. This is extremely useful for testing smart contracts that interact with different blockchain networks. In this tutorial, we'll explore how to set up and run tests on multiple chains using Foundry's vm.createFork and vm.selectFork functions.

Setting Up Test Files

Scenario

We have two test files:

1. VaultL1.t.sol: Tests a vault strategy against Uniswap V3 on Ethereum mainnet.

2. VaultL2.t.sol: Tests the same strategy on a lending protocol on Polygon zkEVM.

Creating Forks and Selecting Networks

For Ethereum Mainnet (VaultL1.t.sol)

// SPDX-License-Identifier: MIT
pragma solidity 0.8.17;

import {Test} from "forge-std/Test.sol";

contract VaultL1Test is Test {
    string ETH_RPC_URL = vm.envString("ETH_RPC_URL");

    function setUp() public {
        uint256 mainnetFork = vm.createFork(ETH_RPC_URL);
        vm.selectFork(mainnetFork);
        // Your setup code here
    }
    // Your tests here
}

For Polygon zkEVM (VaultL2.t.sol)

// SPDX-License-Identifier: MIT
pragma solidity 0.8.17;

import {Test} from "forge-std/Test.sol";

contract VaultL2Test is Test {
    string ZKEVM_RPC_URL = vm.envString("ZKEVM_RPC_URL");

    function setUp() public {
        uint256 zkEvmFork = vm.createFork(ZKEVM_RPC_URL);
        vm.selectFork(zkEvmFork);
        // Your setup code here
    }
    // Your tests here
}

Setting Up .env

Create a .env file in the root directory:

ETH_RPC_URL="your_ethereum_rpc_url_here"
ZKEVM_RPC_URL="your_polygon_zkevm_rpc_url_here"

Running the Tests

With the setup complete, executing forge test will automatically select the appropriate network as specified in the test files. This allows for convenient validation across different chains without needing separate projects.

Benefits

• Cross-chain Testing: Validates contract interaction across various chains.

• Organized Development: Maintains a single project for multi-chain testing.

• Efficiency: Simplifies the testing process with automated network selection.

Real-World Examples

Check out how this setup is used in real-world projects:

• L1Escrow.t.sol

• L2Dai.t.sol

Conclusion

Foundry's ability to handle tests across multiple chains is a powerful feature for smart contract developers. It enhances the testing process, ensuring that contracts work correctly in various blockchain environments.