Hardhat测试报错：Cannot read properties of undefined (reading 'getContract')

问题描述 #

执行yarn hardhat test测试FundMe合约时触发以下错误：

TypeError: Cannot read properties of undefined (reading 'getContract')
错误定位至test\unit\FundMe.test.js第20行。同时VS Code提示Property 'getContract' may not exist on type 'typeof import'，确认导入的ethers对象中不存在该方法。

核心测试代码片段：

const {deployments, ethers, getNamedAccounts } = require("hardhat")
const {assert } = require("chai")

describe("FundMe", async function () {
    let fundMe
    let deployer
    let mockV3Aggregator
    beforeEach(async function() {
       const {deployer} = await getNamedAccounts()
        await deployments.fixture(['all']) 
       fundMe = await ethers.getContract("FundMe", deployer) // 错误触发行
       mockV3Aggregator = await ethers.getContract("MockV3Aggregator", deployer)
    }) 
   // ... 测试用例
})

当前开发依赖：

"devDependencies": {
"@ethersproject/abi": "^5.7.0",
"@ethersproject/providers": "^5.7.2",
"@nomicfoundation/hardhat-chai-matchers": "^1.0.6",
"@nomicfoundation/hardhat-network-helpers": "^1.0.8",
"@nomicfoundation/hardhat-toolbox": "^2.0.1",
"@nomiclabs/hardhat-ethers": "^2.2.2",
"@nomiclabs/hardhat-etherscan": "^3.1.6",
"@typechain/ethers-v5": "^10.2.0",
"@typechain/hardhat": "^6.1.5",
"chai": "^4.3.7",
"ethers": "5.7.2",
"hardhat": "^2.12.7",
"hardhat-deploy": "^0.11.23",
}

问题根源 #

ethers.getContract并非原生Ethers.js的内置方法，而是hardhat-deploy插件为Hardhat的ethers对象扩展的专属功能。错误的主要诱因：

1. Hardhat配置文件未正确引入hardhat-deploy插件，导致扩展方法未生效；
2. 依赖版本冲突，hardhat-deploy与hardhat-ethers的兼容性问题导致扩展方法无法被识别。

解决方案 #

1. 确认Hardhat配置中引入hardhat-deploy #

打开hardhat.config.js，确保顶部已添加插件引入：

require("hardhat-deploy");
require("@nomicfoundation/hardhat-toolbox");
// 其他配置项...

若使用TypeScript，需改为：

import "hardhat-deploy";
import "@nomicfoundation/hardhat-toolbox";
// 其他配置项...

2. 改用hardhat-deploy标准方式获取合约 #

若插件已配置但仍报错，可直接通过deployments对象获取合约部署信息，再连接到指定签名者：

beforeEach(async function() {
   // 修复局部变量覆盖问题，给外部deployer变量赋值
   deployer = (await getNamedAccounts()).deployer;
   await deployments.fixture(['all']);
   
   // 通过deployments.get获取合约元数据，再用getContractAt连接签名者
   const fundMeDeployment = await deployments.get("FundMe");
   fundMe = await ethers.getContractAt(fundMeDeployment.abi, fundMeDeployment.address, deployer);
   
   const mockDeployment = await deployments.get("MockV3Aggregator");
   mockV3Aggregator = await ethers.getContractAt(mockDeployment.abi, mockDeployment.address, deployer);
})

3. 解决依赖冲突 #

@nomicfoundation/hardhat-toolbox已内置@nomiclabs/hardhat-ethers，而hardhat-deploy自带适配的ethers集成，重复依赖会导致冲突。执行以下命令清理冲突：

yarn remove @nomiclabs/hardhat-ethers
yarn install

额外注意事项 #

测试代码中beforeEach内的const {deployer}是局部变量，会覆盖外部声明的deployer变量，导致其始终为undefined，需改为deployer = (await getNamedAccounts()).deployer完成赋值。

内容的提问来源于stack exchange，提问作者Paul Bradley