ERC20标准函数简介与测试方法

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    ERC20是以太坊上的一种合约标准，它包含5个函数、2个事件。具体如下：

  • totalSupply()： token的总量
  • balanceOf() ：某个地址上的余额
  • transfer() ： 发送token
  • allowance() ：额度、配额、津贴
  • approve() ： 批准给某个地址一定数量的token(授予额度、授予津贴)
  • transferFrom()： 提取approve授予的token(提取额度、提取津贴)
  • Transfer() ： token转移事件
  • Approval() ：额度批准事件
标准函数含义
totalSupply()代币总量
balanceOf(addresss account)account地址上的余额
transfer(address recipient, uint256 amount)向recipient发送amount个代币
allowance(address owner, address spender)查询owner给spender的额度(总配额)
approve(address spender, uint256 amount)批准给spender的额度为amount(当前配额)
transferFrom(address sender, address recipient, uint256 amount)recipient提取sender给自己的额度
Transfer(address indexed from, address indexed to, uint256 value)代币转移事件：从from到to转移value个代币
Approval(address indexed owner, address indexed spender, uint256 value)额度批准事件：owner给spender的额度为value

1、ERC20标准接口

interface IERC20 {
    function totalSupply() external view returns (uint256);
    function balanceOf(address account) external view returns (uint256);
    function transfer(address recipient, uint256 amount) external returns (bool);
    function allowance(address owner, address spender) external view returns (uint256);
    function approve(address spender, uint256 amount) external returns (bool);
    function transferFrom(address sender, address recipient, uint256 amount) external returns (bool);

    event Transfer(address indexed from, address indexed to, uint256 value);
    event Approval(address indexed owner, address indexed spender, uint256 value);
}

2、Token实现

    HelloWorldToken合约，它继承IERC20接口，同时添加了name()、decimal()、increaseAllowance()、decreaseAllowance() 等函数。

扩展函数名义
name()代币名称
decimal()代币精度
increaseAllowance()增加额度
decreaseAllowance()减少额度

    //HelloWorldToken.sol

// SPDX-License-Identifier: MIT
pragma solidity >=0.6.0 <0.8.0;

interface IERC20 {
    function totalSupply() external view returns (uint256);
    function balanceOf(address account) external view returns (uint256);
    function transfer(address recipient, uint256 amount) external returns (bool);
    function allowance(address owner, address spender) external view returns (uint256);
    function approve(address spender, uint256 amount) external returns (bool);
    function transferFrom(address sender, address recipient, uint256 amount) external returns (bool);

    event Transfer(address indexed from, address indexed to, uint256 value);
    event Approval(address indexed owner, address indexed spender, uint256 value);
}

library SafeMath {
    function add(uint256 a,uint256 b) internal pure returns (uint256) {
        uint256 c = a+b;
        require(c >= a, "SafeMath: addition overflow");
        return c;
    }

    function sub(uint256 a,uint256 b) internal pure returns (uint256){
        require( b <= a,"SafeMath: subtraction overflow");
        uint256 c = a - b;
        return c;
    }

    function mul(uint256 a,uint256 b) internal pure returns (uint256) {
        if(a == 0) {
            return 0;
        }
        uint256 c = a*b;
        require(c / a == b, "SafeMath: multiplication overflow");
        return c;        
    }
    function div(uint256 a, uint256 b) internal pure returns (uint256) {
        // return div(a,b,"SafeMath: division by zero");
        require(b > 0, "SafeMath: division by zero");
        uint256 c = a / b;
        return c;
    }
    function mod(uint256 a, uint256 b) internal pure returns (uint256) {
        require(b != 0, "SafeMath: modu by zero");
        return a % b;
    }
}

contract HelloWorldToken is IERC20 {
    using SafeMath for uint256;
    string private _name;
    string private _symbol;
    uint8  private _decimal;
    uint256 private _totalSupply;
    mapping (address => uint256) private _balanceOf;
    mapping (address => mapping(address => uint256)) private _allowances;

    constructor(string memory name,string memory symbol,uint8 decimal,uint256 initSupply) public {
        _name = name;
        _symbol = symbol;
        _decimal = decimal;
        _totalSupply = initSupply*(10**uint256(decimal));
        _balanceOf[msg.sender] = _totalSupply;
    }

    function name() external view returns (string memory) {
        return _name;
    }

    function symbol() external view returns (string memory) {
        return _symbol;
    }

    function totalSupply() external override view returns (uint256) {
        return _totalSupply;
    }

    function balanceOf(address account) external override view returns (uint256) {
        return _balanceOf[account];
    }

    function transfer(address recipient,uint256 amount) external override returns (bool) {
        _transfer(msg.sender,recipient,amount);
        return true;
    }

    function _transfer(address sender,address recipient,uint256 amount) internal {
        require(sender != address(0),"ERC20: tranfer from the zero address");
        require(recipient != address(0),"ERC20: tranfer to the zero address");

        _balanceOf[sender] = _balanceOf[sender].sub(amount);
        _balanceOf[recipient] = _balanceOf[recipient].add(amount);
        emit Transfer(sender, recipient, amount);
    }

    function allowance(address owner, address spender) public override view returns (uint256) {
        return _allowances[owner][spender];
    }

    function approve(address spender, uint256 amount) public override returns (bool) {
        _approve(msg.sender,spender,amount);
        return true;
    } 

    function _approve(address owner,address spender,uint256 amount) internal {
        require(owner != address(0),"ERC20: tranfer from the zero address");
        require(spender != address(0),"ERC20: tranfer to the zero address");

        _allowances[owner][spender] = amount;
        emit Approval(owner,spender,amount);
    }

    function transferFrom(address sender, address recipient, uint256 amount) external override returns (bool) {
        _transfer(sender,recipient,amount);
        _approve(sender,msg.sender,_allowances[sender][msg.sender].sub(amount));
        return true;
    }  

    function increaseAllowance(address spender,uint256 amount) public returns (bool) {
        _approve(msg.sender,spender,_allowances[msg.sender][spender].add(amount));
    }

    function decreaseAllowance(address spender,uint256 amount) public returns (bool) {
        _approve(msg.sender,spender,_allowances[msg.sender][spender].sub(amount));
    }

}

3、测试方法

    这里在hardhat里测试ERC20合约。

3.1 创建工程

    a) 打开黑框框，依次输入如下命令

mkdir bcghat
cd bcghat 
npm init -y

    b) 修改package.json，主要是修改devDependencies字段
    //package.json

{
  "name": "bcghat",
  "version": "1.0.0",
  "description": "",
  "main": "",
  "scripts": {
    "test": "echo \\"Error: no test specified\\" && exit 1"
  },
  "keywords": [],
  "author": "",
  "license": "ISC",
  "devDependencies": {
    "@nomiclabs/hardhat-ethers": "^2.0.2",
    "@nomiclabs/hardhat-waffle": "^2.0.1",
    "chai": "^4.3.4",
    "ethereum-waffle": "^3.4.0",
    "ethers": "^5.4.7",
    "hardhat": "^2.6.5",
    "@openzeppelin/contracts": "^3.4.2",
    "typescript": "^4.4.4"
  }
}

    c) 安装依赖包

npm install

    d) 初始化工程

npx hardhat
## 在弹出的下列栏中选中"create simple project"

    e）在bcghat/contracts目录，新建HelloworldToken.sol文件，把上面第2章节的代码拷贝到该文件即可。

touch HelloworldToken.sol

3.2 编写测试脚本

    在bcghat/test目录，新建一个文件夹名称为erc20，然后在erc20里，新建一个文件名称为1.HWToken.js

cd bcghat 
mkdir -p test/erc20
cd test/erc20
touch 1.HWToken.js

测试脚本：1.HWToken.js 内容如下
// 1.HWToken.js

// We import Chai to use its asserting functions here.
const { BigNumber } = require("@ethersproject/bignumber");
const { expect } = require("chai");


describe("Token contract", function () {

  let Factory;
  let hardhatToken;
  let owner;
  let addr1,addr2,addr3;
  let addrs;

  before(async function () {
    // Get the ContractFactory and Signers here.
    Factory = await ethers.getContractFactory("HelloWorldToken",{from:owner});
    [owner, addr1, addr2, addr3, ...addrs] = await ethers.getSigners();

    // Token名称：HWToken
    // Token符号: HWT
    // Token精度: 18
    // Token总量: 10000枚
    hardhatToken = await Factory.deploy("HWToken","HWT","18",10000);
    console.log('owner:',owner.address);
    console.log('token:',hardhatToken.address);
  });

  // You can nest describe calls to create subsections.
  describe("Deployment", function () {
    it("Check name", async () => {
      expect(await hardhatToken.name()).to.equal("HWToken");
    });

    it("Check symbol", async () => {
        expect(await hardhatToken.symbol()).to.equal("HWT");
    });

    it("Check totalSupply", async () => {
      const totalSupply = await hardhatToken.balanceOf(owner.address);
      expect(await hardhatToken.totalSupply()).to.equal(totalSupply);
    });

    it("Check transfer", async () => {
      await hardhatToken.transfer(addr1.address,100);
      expect(await hardhatToken.balanceOf(addr1.address)).to.equal(100)
    })

    it("check the event of transfer",async () => {
      await expect(hardhatToken.transfer(addr1.address, 100))
        .to.emit(hardhatToken,'Transfer')
        .withArgs(owner.address,addr1.address,100);
    });

    it("check approve",async () => {
      //addr2获取200配额
      await hardhatToken.approve(addr2.address,200);
      expect(await hardhatToken.allowance(owner.address,addr2.address)).to.equal(200);
    })

    it("check increaseAllowance", async () => {
      //owner继续给addr2追加300配额，addr2现在有200+300=500配额
      await hardhatToken.increaseAllowance(addr2.address,300);
      expect(await hardhatToken.allowance(owner.address,addr2.address)).to.equal(500);
    })

    it("check transferFrom", async () => {      
       //addr2提取属owner给自己的50个配额，剩余500-50=450
      await hardhatToken.connect(addr2).transferFrom(owner.address,addr2.address,50);
      expect(await hardhatToken.allowance(owner.address,addr2.address)).to.equal(450);
    })

    it("check decreaseAllowance", async () => {
      //减少addr2的100个配额，还剩下450-100 = 350
      await hardhatToken.decreaseAllowance(addr2.address,100);
      expect(await hardhatToken.allowance(owner.address,addr2.address)).to.equal(350);
    })

    it("can not transfer above the amount", async () => {
      //addr1只有100份token，却要发送1007份，超过余额，交易会重置
      await expect(hardhatToken.connect(addr1).transfer(addr3.address, 1007)).to.be.reverted;
    })

  });
 
});

3.3 编译并测试

    a) 编译合约

npx hardhat compile

    b) 测试合约

npx hardhat test test/erc20/1.HWToken.js

    效果如下：

图(1) 用hardhat测试合约

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