readme.md

run forge test --mc POCTest -vvvvv to test

poc.t.sol

// SPDX-License-Identifier: MIT
pragma solidity ^0.7.6;
pragma experimental ABIEncoderV2;

import {Test, console} from "forge-std/Test.sol";
import {PuppyRaffle} from "../src/PuppyRaffle.sol";
import {Attackpuppy} from "./attacker.sol";

contract POCTest is Test {
    PuppyRaffle puppyRaffle;
    uint256 entranceFee = 1e18;
    address playerOne = address(1);
    address playerTwo = address(2);
    address playerThree = address(3);
    address playerFour = address(4);
    address feeAddress = address(99);
    uint256 duration = 1 days;

    ///// attacker
    Attackpuppy attacker;

    function setUp() public {
        puppyRaffle = new PuppyRaffle(entranceFee, feeAddress, duration);
        attacker = new Attackpuppy(address(puppyRaffle));
    }

    //////////////////////
    /// selectWinner         ///
    /////////////////////
    modifier playersEntered() {
        address[] memory players = new address[](4);
        players[0] = playerOne;
        players[1] = playerTwo;
        players[2] = playerThree;
        players[3] = playerFour;
        puppyRaffle.enterRaffle{value: entranceFee * 4}(players);
        _;
    }

    function testWithdrawFees() public playersEntered {
        vm.warp(block.timestamp + duration + 1);
        vm.roll(block.number + 1);

        uint256 expectedPrizeAmount = ((entranceFee * 4) * 20) / 100;
        puppyRaffle.changeFeeAddress(address(0));

        puppyRaffle.selectWinner();
        puppyRaffle.withdrawFees();
        assertEq(address(0).balance, expectedPrizeAmount);
    }
}