openzeppelin-contracts/test/token/ERC20/ERC20.test.js

const { ethers } = require('hardhat');
const { expect } = require('chai');
const { loadFixture } = require('@nomicfoundation/hardhat-network-helpers');
const { PANIC_CODES } = require('@nomicfoundation/hardhat-chai-matchers/panic');

const {
  shouldBehaveLikeERC20,
  shouldBehaveLikeERC20Transfer,
  shouldBehaveLikeERC20Approve,
} = require('./ERC20.behavior');

const TOKENS = [{ Token: '$ERC20' }, { Token: '$ERC20ApprovalMock', forcedApproval: true }];

const name = 'My Token';
const symbol = 'MTKN';
const initialSupply = 100n;

describe('ERC20', function () {
  for (const { Token, forcedApproval } of TOKENS) {
    describe(Token, function () {
      const fixture = async () => {
        // this.accounts is used by shouldBehaveLikeERC20
        const accounts = await ethers.getSigners();
        const [holder, recipient] = accounts;

        const token = await ethers.deployContract(Token, [name, symbol]);
        await token.$_mint(holder, initialSupply);

        return { accounts, holder, recipient, token };
      };

      beforeEach(async function () {
        Object.assign(this, await loadFixture(fixture));
      });

      shouldBehaveLikeERC20(initialSupply, { forcedApproval });

      it('has a name', async function () {
        expect(await this.token.name()).to.equal(name);
      });

      it('has a symbol', async function () {
        expect(await this.token.symbol()).to.equal(symbol);
      });

      it('has 18 decimals', async function () {
        expect(await this.token.decimals()).to.equal(18n);
      });

      describe('_mint', function () {
        const value = 50n;
        it('rejects a null account', async function () {
          await expect(this.token.$_mint(ethers.ZeroAddress, value))
            .to.be.revertedWithCustomError(this.token, 'ERC20InvalidReceiver')
            .withArgs(ethers.ZeroAddress);
        });

        it('rejects overflow', async function () {
          await expect(this.token.$_mint(this.recipient, ethers.MaxUint256)).to.be.revertedWithPanic(
            PANIC_CODES.ARITHMETIC_UNDER_OR_OVERFLOW,
          );
        });

        describe('for a non zero account', function () {
          beforeEach('minting', async function () {
            this.tx = await this.token.$_mint(this.recipient, value);
          });

          it('increments totalSupply', async function () {
            await expect(await this.token.totalSupply()).to.equal(initialSupply + value);
          });

          it('increments recipient balance', async function () {
            await expect(this.tx).to.changeTokenBalance(this.token, this.recipient, value);
          });

          it('emits Transfer event', async function () {
            await expect(this.tx).to.emit(this.token, 'Transfer').withArgs(ethers.ZeroAddress, this.recipient, value);
          });
        });
      });

      describe('_burn', function () {
        it('rejects a null account', async function () {
          await expect(this.token.$_burn(ethers.ZeroAddress, 1n))
            .to.be.revertedWithCustomError(this.token, 'ERC20InvalidSender')
            .withArgs(ethers.ZeroAddress);
        });

        describe('for a non zero account', function () {
          it('rejects burning more than balance', async function () {
            await expect(this.token.$_burn(this.holder, initialSupply + 1n))
              .to.be.revertedWithCustomError(this.token, 'ERC20InsufficientBalance')
              .withArgs(this.holder, initialSupply, initialSupply + 1n);
          });

          const describeBurn = function (description, value) {
            describe(description, function () {
              beforeEach('burning', async function () {
                this.tx = await this.token.$_burn(this.holder, value);
              });

              it('decrements totalSupply', async function () {
                expect(await this.token.totalSupply()).to.equal(initialSupply - value);
              });

              it('decrements holder balance', async function () {
                await expect(this.tx).to.changeTokenBalance(this.token, this.holder, -value);
              });

              it('emits Transfer event', async function () {
                await expect(this.tx).to.emit(this.token, 'Transfer').withArgs(this.holder, ethers.ZeroAddress, value);
              });
            });
          };

          describeBurn('for entire balance', initialSupply);
          describeBurn('for less value than balance', initialSupply - 1n);
        });
      });

      describe('_update', function () {
        const value = 1n;

        beforeEach(async function () {
          this.totalSupply = await this.token.totalSupply();
        });

        it('from is the zero address', async function () {
          const tx = await this.token.$_update(ethers.ZeroAddress, this.holder, value);
          await expect(tx).to.emit(this.token, 'Transfer').withArgs(ethers.ZeroAddress, this.holder, value);

          expect(await this.token.totalSupply()).to.equal(this.totalSupply + value);
          await expect(tx).to.changeTokenBalance(this.token, this.holder, value);
        });

        it('to is the zero address', async function () {
          const tx = await this.token.$_update(this.holder, ethers.ZeroAddress, value);
          await expect(tx).to.emit(this.token, 'Transfer').withArgs(this.holder, ethers.ZeroAddress, value);

          expect(await this.token.totalSupply()).to.equal(this.totalSupply - value);
          await expect(tx).to.changeTokenBalance(this.token, this.holder, -value);
        });

        describe('from and to are the same address', function () {
          it('zero address', async function () {
            const tx = await this.token.$_update(ethers.ZeroAddress, ethers.ZeroAddress, value);
            await expect(tx).to.emit(this.token, 'Transfer').withArgs(ethers.ZeroAddress, ethers.ZeroAddress, value);

            expect(await this.token.totalSupply()).to.equal(this.totalSupply);
            await expect(tx).to.changeTokenBalance(this.token, ethers.ZeroAddress, 0n);
          });

          describe('non zero address', function () {
            it('reverts without balance', async function () {
              await expect(this.token.$_update(this.recipient, this.recipient, value))
                .to.be.revertedWithCustomError(this.token, 'ERC20InsufficientBalance')
                .withArgs(this.recipient, 0n, value);
            });

            it('executes with balance', async function () {
              const tx = await this.token.$_update(this.holder, this.holder, value);
              await expect(tx).to.changeTokenBalance(this.token, this.holder, 0n);
              await expect(tx).to.emit(this.token, 'Transfer').withArgs(this.holder, this.holder, value);
            });
          });
        });
      });

      describe('_transfer', function () {
        beforeEach(function () {
          this.transfer = this.token.$_transfer;
        });

        shouldBehaveLikeERC20Transfer(initialSupply);

        it('reverts when the sender is the zero address', async function () {
          await expect(this.token.$_transfer(ethers.ZeroAddress, this.recipient, initialSupply))
            .to.be.revertedWithCustomError(this.token, 'ERC20InvalidSender')
            .withArgs(ethers.ZeroAddress);
        });
      });

      describe('_approve', function () {
        beforeEach(function () {
          this.approve = this.token.$_approve;
        });

        shouldBehaveLikeERC20Approve(initialSupply);

        it('reverts when the owner is the zero address', async function () {
          await expect(this.token.$_approve(ethers.ZeroAddress, this.recipient, initialSupply))
            .to.be.revertedWithCustomError(this.token, 'ERC20InvalidApprover')
            .withArgs(ethers.ZeroAddress);
        });
      });
    });
  }
});