Patrick Collins Brownie课程中Lottery合约单元测试断言失败求助

在学习Patrick Collins的FreeCodeCamp/Chainlink Brownie/Solidity课程过程中，其余测试均正常通过，但test_can_pick_winner_correctly单元测试出现断言失败。预期第一个参与者（account[0]）成为赢家（因STATIC_RNG=777，777%3=0），但实际合约返回的赢家地址不匹配。

错误信息 #

assert lottery.recentWinner() == account
E       AssertionError: assert '0x33A4622B82D4c04a53e170c638B944ce27cffce3' == <Account '0x66aB6D9362d4F35596279692F0251Db635165871'>
E        +  where '0x33A4622B82D4c04a53e170c638B944ce27cffce3' = <ContractCall 'recentWinner()'>()
E        +    where <ContractCall 'recentWinner()'> = <Lottery Contract '0x6951b5Bd815043E3F842c1b026b0Fa888Cc2DD85'>.recentWinner

错误位置：tests\test_lottery_unit.py:85: AssertionError

相关代码 #

单元测试代码 #

from brownie import Lottery, accounts, config, network, exceptions
from scripts.helpful_scripts import (
    LOCAL_BLOCKCHAIN_ENVIRONMENTS,
    get_account,
    fund_with_link,
    get_contract,
)
from scripts.deploy_lottery import deploy_lottery
from web3 import Web3
import pytest

def test_can_pick_winner_correctly():
    # Arrange
    if network.show_active() not in LOCAL_BLOCKCHAIN_ENVIRONMENTS:
        pytest.skip()
    lottery = deploy_lottery()
    account = get_account()
    lottery.startLottery({"from": account})
    lottery.enter({"from": account, "value": lottery.getEntranceFee()})
    lottery.enter({"from": get_account(index=1), "value": lottery.getEntranceFee()})
    lottery.enter({"from": get_account(index=2), "value": lottery.getEntranceFee()})
    fund_with_link(lottery)
    transaction = lottery.endLottery({"from": account})
    request_id = transaction.events["RequestedRandomness"]["requestId"]
    STATIC_RNG = 777
    get_contract("vrf_coordinator").callBackWithRandomness(
        request_id, STATIC_RNG, lottery.address, {"from": account}
    )
    starting_balance_of_account = account.balance()
    balance_of_lottery = lottery.balance()
    # 777 % 3 = 0
    assert lottery.recentWinner() == account
    assert lottery.balance() == 0
    assert account.balance() == starting_balance_of_account + balance_of_lottery

部署脚本deploy_lottery.py #

from dis import show_code

from pkg_resources import ensure_directory
from scripts.helpful_scripts import get_account, get_contract, fund_with_link
from brownie import Lottery, network, config
import time


def deploy_lottery():
    account = get_account()
    lottery = Lottery.deploy(
        get_contract("eth_usd_price_feed").address,
        get_contract("vrf_coordinator").address,
        get_contract("link_token").address,
        config["networks"][network.show_active()]["fee"],
        config["networks"][network.show_active()]["keyhash"],
        {"from": account},
        publish_source=config["networks"][network.show_active()].get("verify", False),
    )
    print("Deployed Lottery!")
    return lottery


def start_lottery():
    account = get_account()
    lottery = Lottery[-1]
    starting_tx = lottery.startLottery({"from": account})
    starting_tx.wait(1)
    print("The lottery has started")


def enter_lotter():
    account = get_account()
    lottery = Lottery[-1]
    value = lottery.getEntranceFee() + 10000000
    tx = lottery.enter({"from": account, "value": value})
    tx.wait(1)
    print("You entered the lottery!")


def end_lottery():
    account = get_account()
    lottery = Lottery[-1]
    # fund the contract and then end the lottery
    tx = fund_with_link(lottery.address)
    tx.wait(1)
    ending_transaction = lottery.endLottery({"from": account})
    ending_transaction.wait(1)
    time.sleep(60)
    print(f"{lottery.recentWinner()} is the new winner!")


def main():
    deploy_lottery()
    start_lottery()
    enter_lotter()
    end_lottery()

Solidity合约代码 #

pragma solidity >=0.7.0 <0.8.7;

import "@chainlink/contracts/src/v0.7/interfaces/AggregatorV3Interface.sol";
import "@openzeppelin/contracts/access/Ownable.sol";
import "@chainlink/contracts/src/v0.7/VRFConsumerBase.sol";

contract Lottery is VRFConsumerBase, Ownable {
    address payable[] public players;
    uint256 public usdEntryFee;
    AggregatorV3Interface internal ethUsdPriceFeed;
    enum LOTTERY_STATE {
        OPEN,
        CLOSED,
        CALCULATING_WINNER
    }
    LOTTERY_STATE public lottery_state;
    uint256 public fee;
    bytes32 public keyhash;
    event RequestedRandomness(bytes32 requestId);
    address payable public recentWinner;
    uint256 public randomness;

    constructor(
        address _priceFeedAddress,
        address _vrfCoordinator,
        address _link,
        uint256 _fee,
        bytes32 _keyhash
    ) public VRFConsumerBase(_vrfCoordinator, _link) {
        usdEntryFee = 50 * (10**18);
        ethUsdPriceFeed = AggregatorV3Interface(_priceFeedAddress);
        lottery_state = LOTTERY_STATE.CLOSED;
        fee = _fee;
        keyhash = _keyhash;
    }

    function enter() public payable {
        require(lottery_state == LOTTERY_STATE.OPEN);
        require(msg.value >= getEntranceFee(), "Not enough ETH!");
        players.push(msg.sender);
    }

    function getEntranceFee() public view returns (uint256) {
        (, int256 price, , , ) = ethUsdPriceFeed.latestRoundData();
        uint256 adjustedPrice = uint256(price) * (10**10); //18 decimals
        uint256 costToEnter = (usdEntryFee * 10**18) / adjustedPrice;
        return costToEnter;
    }

    function startLottery() public onlyOwner {
        require(
            lottery_state == LOTTERY_STATE.CLOSED,
            "Can't start a new lottery yet!"
        );
        lottery_state = LOTTERY_STATE.OPEN;
    }

    function endLottery() public onlyOwner {
        lottery_state = LOTTERY_STATE.CALCULATING_WINNER;
        bytes32 requestId = requestRandomness(keyhash, fee);
        emit RequestedRandomness(requestId);
    }

    function fulfillRandomness(bytes32 _requestId, uint256 _randomness)
        internal
        override
    {
        require(
            lottery_state == LOTTERY_STATE.CALCULATING_WINNER,
            "You aren't there yet!"
        );
        require(_randomness > 0, "random-not-found");
        uint256 indexOfWinner = _randomness & players.length;
        recentWinner = players[indexOfWinner];
        recentWinner.transfer(address(this).balance);
        players = new address payable[](0);
        lottery_state = LOTTERY_STATE.CLOSED;
        randomness = _randomness;
    }
}

问题排查与修复 #

问题出在Solidity合约的fulfillRandomness函数中，计算赢家索引时误用了位运算符&而非取余运算符%：

• 预期计算：777 % 3 = 0，对应第一个参与者
• 实际计算：777 & 3 = 1，对应第二个参与者

修改fulfillRandomness函数中的索引计算代码，将&替换为%即可修复：

function fulfillRandomness(bytes32 _requestId, uint256 _randomness)
    internal
    override
{
    require(
        lottery_state == LOTTERY_STATE.CALCULATING_WINNER,
        "You aren't there yet!"
    );
    require(_randomness > 0, "random-not-found");
    uint256 indexOfWinner = _randomness % players.length; // 替换为取余运算符
    recentWinner = players[indexOfWinner];
    recentWinner.transfer(address(this).balance);
    players = new address payable[](0);
    lottery_state = LOTTERY_STATE.CLOSED;
    randomness = _randomness;
}

内容的提问来源于stack exchange，提问作者USCMigs