foundry-testing

Foundry Testing Patterns

Test File Template

// SPDX-License-Identifier: MIT
pragma solidity ^0.8.20;

import {Test, console2} from "forge-std/Test.sol";
import {MyContract} from "../src/MyContract.sol";
import {IERC20} from "@openzeppelin/contracts/token/ERC20/IERC20.sol";

contract MyContractTest is Test {
    MyContract public target;
    address public alice = makeAddr("alice");
    address public bob = makeAddr("bob");
    address public deployer = makeAddr("deployer");

    function setUp() public {
        vm.startPrank(deployer);
        target = new MyContract();
        vm.stopPrank();

        vm.deal(alice, 100 ether);
        vm.deal(bob, 100 ether);
    }

    function test_basicOperation() public {
        vm.prank(alice);
        target.doSomething(42);
        assertEq(target.value(), 42);
    }

    function test_revertOnUnauthorized() public {
        vm.prank(bob);
        vm.expectRevert("unauthorized");
        target.adminFunction();
    }
}

Essential Cheatcodes

Identity & Balance

// Set msg.sender for next call
vm.prank(alice);

// Set msg.sender for all subsequent calls until stopPrank()
vm.startPrank(alice);
// ... multiple calls as alice
vm.stopPrank();

// Set ETH balance
vm.deal(alice, 100 ether);

// Set ERC20 balance (writes to storage slot)
deal(address(usdc), alice, 1_000_000e6);

// Create labeled address
address alice = makeAddr("alice");

// Create address with private key
(address signer, uint256 pk) = makeAddrAndKey("signer");

Time & Block Manipulation

// Set block.timestamp
vm.warp(1700000000);

// Set block.number
vm.roll(18_000_000);

// Skip forward in time
skip(1 days);

// Rewind time
rewind(1 hours);

Revert Expectations

// Expect next call to revert with message
vm.expectRevert("insufficient balance");
target.withdraw(1000);

// Expect revert with custom error
vm.expectRevert(abi.encodeWithSelector(InsufficientBalance.selector, 1000, 500));
target.withdraw(1000);

// Expect revert with no message check
vm.expectRevert();
target.failingFunction();