_Follow along with the video lesson:_ --- ### Exploit - Storage Collision - PoC Alright! Let's see what a storage collision proof of code looks like. Honestly, it's not too difficult at all. Start by importing ThunderLoanUpgraded.sol into our ThunderLoanTest.t.sol. ```js import { ThunderLoanUpgraded } from "../../src/upgradedProtocol/ThunderLoanUpgraded.sol"; ``` Then we can add our test, right at the bottom. Let's consider what we need to accomplish. 1. Acquire the fee before the upgrade 2. Deploy ThunderLoanUpgraded.sol 3. Upgrade to new implementation 4. Acquire the fee after the upgrade 5. Assert Shouldn't be too difficult! ```js function testUpgradeBreaksFee() public setAllowedToken hasDeposits { uint256 feeBeforeUpgrade = thunderLoan.getFee(); vm.startPrank(thunderLoan.owner()); ThunderLoanUpgraded upgraded = new ThunderLoanUpgraded(); thunderLoan.upgradeToAndCall(address(upgraded), ""); uint256 feeAfterUpgrade = thunderLoan.getFee(); vm.stopPrank(); console2.log("Fee before upgrade:", feeBeforeUpgrade); console2.log("Fee after upgrade:", feeAfterUpgrade); assert(feeBeforeUpgrade != feeAfterUpgrade); } ``` Now, if we run this test... ```bash forge test --mt testUpgradeBreaksFee -vvv ``` ::image{src='/security-section-6/46-exploit-storage-collision-poc/exploit-storage-collision-poc1.png' style='width: 100%; height: auto;'} Holy Cow, there it is. Another High severity finding! Let's walk through doing the last write up of this security review, in the next lesson. We're almost there!