Simple auction solidity

Auction.sol

// SPDX-License-Identifier: GPL-3.0
pragma solidity ^0.8.4;

contract SimpleAuction {
    address payable public beneficiary;
    uint public auctionEndTime;

    address public highestBidder;
    uint public highestBid;

    mapping(address => uint) pendingReturns;

    bool ended;

    event HighestBidIncreased(address bidder, uint amount);
    event AuctionEnded(address winner, uint amount);

    error AuctionAlreadyEnded();
    error BidNotHighEnough(uint highestBid);
    error AuctionNotYetEnded(uint timeToAuctionEnd);
    error AuctionEndAlreadyCalled();

    constructor(
        uint biddingTime,
        address payable beneficiaryAddress
    ) {
        beneficiary = beneficiaryAddress;
        auctionEndTime = block.timestamp + biddingTime;
    }

    function bid() external payable {

        if (block.timestamp > auctionEndTime)
            revert AuctionAlreadyEnded();

        if (msg.value <= highestBid)
            revert BidNotHighEnough(highestBid);

        if (highestBid != 0) {
            pendingReturns[highestBidder] += highestBid;
        }
        highestBidder = msg.sender;
        highestBid = msg.value;
        emit HighestBidIncreased(msg.sender, msg.value);
    }

    function withdraw() external returns (bool) {
        uint amount = pendingReturns[msg.sender];
        if (amount > 0) {
            pendingReturns[msg.sender] = 0;

            if (!payable(msg.sender).send(amount)) {
                pendingReturns[msg.sender] = amount;
                return false;
            }
        }
        return true;
    }

    function auctionEnd() external {

        if (block.timestamp < auctionEndTime)
            revert AuctionNotYetEnded(auctionEndTime - block.timestamp);
        if (ended)
            revert AuctionEndAlreadyCalled();

        ended = true;
        emit AuctionEnded(highestBidder, highestBid);

        beneficiary.transfer(highestBid);
    }
}