20-TokenBank.test.ts

import { SignerWithAddress } from '@nomiclabs/hardhat-ethers/signers';
import { expect } from 'chai';
import { Contract } from 'ethers';
import { ethers } from 'hardhat';
const { utils } = ethers;

const TOTAL_TOKENS_SUPPLY = 1000000;

describe('TokenBankChallenge', () => {
  let target: Contract;
  let token: Contract;
  let attacker: SignerWithAddress;
  let deployer: SignerWithAddress;

  before(async () => {
    [attacker, deployer] = await ethers.getSigners();

    const [targetFactory, tokenFactory] = await Promise.all([
      ethers.getContractFactory('TokenBankChallenge', deployer),
      ethers.getContractFactory('SimpleERC223Token', deployer),
    ]);

    target = await targetFactory.deploy(attacker.address);

    await target.deployed();

    const tokenAddress = await target.token();

    token = await tokenFactory.attach(tokenAddress);

    await token.deployed();

    target = target.connect(attacker);
    token = token.connect(attacker);
  });

  it('exploit', async () => {
    /**
     * YOUR CODE HERE
     * */

    expect(await token.balanceOf(target.address)).to.equal(0);
    expect(await token.balanceOf(attacker.address)).to.equal(
      utils.parseEther(TOTAL_TOKENS_SUPPLY.toString())
    );
  });
});