feat: demonstrate state-preserving V2 upgrade

test/BankInvariant.t.sol

@@ -2,26 +2,45 @@
 pragma solidity 0.8.35;
 
 import {BankTestBase} from "./helpers/BankTestBase.sol";
-import {BankHandler} from "./helpers/BankHandler.sol";
+import {BankV2} from "../src/BankV2.sol";
+import {Options, Upgrades} from "openzeppelin-foundry-upgrades/Upgrades.sol";
+import {BankV2Handler} from "./helpers/BankV2Handler.sol";
 
 contract BankInvariantTest is BankTestBase {
-    BankHandler internal handler;
+    BankV2Handler internal handler;
 
     function setUp() public override {
         super.setUp();
+        Options memory opts;
+        opts.referenceContract = "BankV1.sol:BankV1";
+        Upgrades.upgradeProxy(proxy, "BankV2.sol:BankV2", "", opts, owner);
+        BankV2 bankV2 = BankV2(proxy);
 
-        handler = new BankHandler(token, bank);
+        handler = new BankV2Handler(token, bankV2);
         vm.prank(owner);
         token.transferOwnership(address(handler));
 
         targetContract(address(handler));
-        bytes4[] memory selectors = new bytes4[](3);
+        bytes4[] memory selectors = new bytes4[](4);
         selectors[0] = handler.deposit.selector;
         selectors[1] = handler.withdraw.selector;
         selectors[2] = handler.donate.selector;
+        selectors[3] = handler.transfer.selector;
         targetSelector(FuzzSelector({addr: address(handler), selectors: selectors}));
     }
 
+    function testHandlerExecutesDeterministicTrackedTransfer() public {
+        handler.deposit(0, 40e6);
+
+        handler.transfer(0, 0, 15e6);
+
+        assertEq(bank.balanceOf(handler.actorAt(0)), 25e6);
+        assertEq(bank.balanceOf(handler.actorAt(1)), 15e6);
+        assertEq(handler.ghostTransferred(), 15e6);
+        assertEq(bank.totalLiabilities(), 40e6);
+        assertEq(token.balanceOf(address(bank)), 40e6);
+    }
+
     function invariant_liabilitiesEqualTrackedBalances() public view {
         uint256 sum;
         for (uint256 i; i < handler.actorCount(); ++i) {