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11、Foundry Cheatcodes

Cheatcodes give you powerful testing utilities to manipulate the state of the EVM, mock data, and more.

What are Cheatcodes?​

Cheatcodes are special functions exposed by the vm object in Foundry tests. They allow you to manipulate the blockchain state, mock calls, and perform other testing operations that would be impossible in production.

Common Cheatcodes​

Time Manipulation​

vm.warp(uint256)​

Set block.timestamp to a specific value:

vm.warp(1641070800); // Set to Jan 2, 2022

vm.roll(uint256)​

Set block.number to a specific value:

vm.roll(123456);

Account Manipulation​

vm.prank(address)​

Perform the next call as a different address:

vm.prank(alice);
token.transfer(bob, 100); // This call comes from alice

vm.startPrank(address)​

All subsequent calls come from the specified address until vm.stopPrank():

vm.startPrank(alice);
token.approve(spender, 100);
token.transfer(bob, 50);
vm.stopPrank();

vm.deal(address, uint256)​

Set the ETH balance of an address:

vm.deal(alice, 100 ether);

Expectations​

vm.expectRevert()​

Expect the next call to revert:

vm.expectRevert("Insufficient balance");
token.transfer(bob, 1000);

vm.expectEmit()​

Expect an event to be emitted:

vm.expectEmit(true, true, false, true);
emit Transfer(alice, bob, 100);
token.transfer(bob, 100);

Mocking​

vm.mockCall(address, bytes, bytes)​

Mock the return data of a call:

vm.mockCall(
    address(oracle),
    abi.encodeWithSelector(Oracle.getPrice.selector),
    abi.encode(100)
);

Example Test​

// 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 alice = address(1);
    address bob = address(2);

    function setUp() public {
        token = new Token();
        vm.deal(alice, 100 ether);
        vm.deal(bob, 100 ether);
    }

    function testTransfer() public {
        vm.prank(alice);
        token.transfer(bob, 100);
        
        assertEq(token.balanceOf(bob), 100);
    }

    function testRevertInsufficientBalance() public {
        vm.expectRevert("Insufficient balance");
        vm.prank(alice);
        token.transfer(bob, 1000);
    }
}

Best Practices​

  1. Use setUp(): Initialize your test state in the setUp() function
  2. Clear pranks: Always use vm.stopPrank() after vm.startPrank()
  3. Test edge cases: Use cheatcodes to test boundary conditions
  4. Document complex setups: Comment your cheatcode usage for clarity

Resources​

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