使用 ethers js 运行安全帽测试时，合约事件侦听器不会触发

Question

这是一个非常小的存储库来显示该问题：https ://github.com/adamdry/ethers-event-issue

但我也会在这里解释一下。这是我的合同：

//SPDX-License-Identifier: UNLICENSED;
pragma solidity 0.8.4;

contract ContractA {

    event TokensMinted(uint amount);

    function mint(uint amount) public {
        emit TokensMinted(amount);
    }

}

这是我的测试代码：

import * as chai from 'chai'
import { BigNumber, ContractTransaction } from 'ethers'
import { ethers } from 'hardhat'
import { ContractA, ContractAFactory } from '../typechain'

const expect = chai.expect

describe("Example test", function () {
    it("should fire the event", async function () {
        const [owner] = await ethers.getSigners();

        const contractAFactory = (await ethers.getContractFactory(
            'ContractA',
            owner,
        )) as ContractAFactory

        const contractA: ContractA = await contractAFactory.deploy()

        contractA.on('TokensMinted', (amount: BigNumber) => {
            // THIS LINE NEVER GETS HIT
            console.log('###########')
        })

        const contractTx: ContractTransaction = await contractA.mint(123)
        const contractReceipt: ContractReceipt = await contractTx.wait()

        for (const event of contractReceipt.events!) {
            console.log(JSON.stringify(event))
        }
    });
});

我期望###########将其打印到控制台，但事实并非如此，因此侦听器函数由于某种原因没有被执行。

如果我深入研究 ContractReceipt ，就会发现正确的事件数据：

//SPDX-License-Identifier: UNLICENSED;
pragma solidity 0.8.4;

contract ContractA {

    event TokensMinted(uint amount);

    function mint(uint amount) public {
        emit TokensMinted(amount);
    }

}

Answer 1

完整的答案在这里：https://github.com/nomiclabs/hardhat/issues/1692#issuecomment-905674692

但总而言之，这不起作用的原因是 ethers.js 默认情况下使用轮询来获取事件，轮询间隔为 4 秒。如果您在测试结束时添加此内容：

await new Promise(res => setTimeout(() => res(null), 5000));

该事件应该触发。

然而！您还可以调整给定合约的轮询间隔，如下所示：

// at the time of this writing, ethers' default polling interval is
// 4000 ms. here we turn it down in order to speed up this test.
// see also
// https://github.com/ethers-io/ethers.js/issues/615#issuecomment-848991047
const provider = greeter.provider as EthersProviderWrapper;
provider.pollingInterval = 100;

如下所示：https: //github.com/nomiclabs/hardhat/blob/master/packages/hardhat-ethers/test/index.ts#L642

然而！（再次）如果您想从事件中获取结果，以下方法不需要更改轮询或任何其他基于“时间”的解决方案，根据我的经验，这可能会导致不稳定的测试：

it('testcase', async() => {
  const tx = await contract.transfer(...args); // 100ms
  const rc = await tx.wait(); // 0ms, as tx is already confirmed
  const event = rc.events.find(event => event.event === 'Transfer');
  const [from, to, value] = event.args;
  console.log(from, to, value);
})

这是我的 TypeScriptyfied 版本（根据我自己的合同，事件和参数略有不同）：

const contractTx: ContractTransaction = await tokenA.mint(owner.address, 500)
const contractReceipt: ContractReceipt = await contractTx.wait()
const event = contractReceipt.events?.find(event => event.event === 'TokensMinted')
const amountMintedFromEvent: BigNumber = event?.args!['amount']

这是与上述内容一致的 Solidity 事件声明：

event TokensMinted(uint amount);