--- ### Final Invariant & Tweaks A reminder of where Invariant.t.sol sits currently: <details> <summary>Invariant.t.sol</summary> ```solidity // SPDX-License-Identifier: MIT pragma solidity ^0.8.20; import { Test } from "forge-std/Test.sol"; import { StdInvariant } from "forge-std/StdInvariant.sol"; import { ERC20Mock } from "test/mocks/ERC20Mock.sol"; import { PoolFactory } from "../../src/PoolFactory.sol"; import { TSwapPool } from "../../src/TSwapPool.sol"; contract Invariant is StdInvariant, Test { ERC20Mock poolToken; ERC20Mock weth; PoolFactory factory; TSwapPool pool; // poolToken, weth int256 public constant STARTING_X = 100e18; int256 public constant STARTING_Y = 50e18; function setUp() public { poolToken = new ERC20Mock(); weth = new ERC20Mock(); factory = new PoolFactory(address(weth)); pool = TSwapPool(factory.createPool(address(poolToken))); poolToken.mint(address(this), uint256(STARTING_X)); weth.mint(address(this), uint256(STARTING_Y)); poolToken.approve(address(pool), type(uint256).max); weth.approve(address(pool), type(uint256).max); // Deposit Into Pool pool.deposit(uint256(STARTING_Y), uint256(STARTING_Y), uint256(STARTING_X), uint64(block.timestamp)); } } ``` </details> Now that we have everything set up in our `Handler` we can come back to our `Invariant.t.sol`. Our actual test at this point is going to be surprisingly basic because of all the set up we've done! ```js function statefulFuzz_constantProductFormulaStaysTheSameY() public { assertEq(handler.actualDeltaY(), handler.expectedDeltaY()); } ``` That's literally it. We call `assertEq` and compare our actuals and expecteds for changes in `poolToken` amounts, we'll do one token at a time starting with poolToken. We just need to set up our `Handler` as our target contract now. We'll also set up target function selectors, just like we saw previously. ```js ... import {Handler} from "./Handler.t.sol"; contract Invariant is StdInvariant, Test { ... Handler handler; ... function setUp(){ ... handler = new Handler(pool); bytes4[] memory selectors = new bytes4[](2); selectors[0] = handler.deposit.selector; selectors[1] = handler.swapPoolTokenForWethBasedOnOutputWeth.selector; targetSelector(FuzzSelector({ addr: address(handler), selectors: selectors })); targetContract(address(handler)); } } ``` ### Wrap Up Here's Invariant.t.sol all together before we finally run our test, in the next lesson. ```solidity // SPDX-License-Identifier: MIT pragma solidity ^0.8.20; import { Test } from "forge-std/Test.sol"; import { StdInvariant } from "forge-std/StdInvariant.sol"; import { ERC20Mock } from "test/mocks/ERC20Mock.sol"; import { PoolFactory } from "../../src/PoolFactory.sol"; import { TSwapPool } from "../../src/TSwapPool.sol"; import { Handler } from "./Handler.t.sol"; contract Invariant is StdInvariant, Test { ERC20Mock poolToken; ERC20Mock weth; PoolFactory factory; TSwapPool pool; // poolToken, weth int256 public constant STARTING_X = 100e18; int256 public constant STARTING_Y = 50e18; Handler handler; function setUp() public { poolToken = new ERC20Mock(); weth = new ERC20Mock(); factory = new PoolFactory(address(weth)); pool = TSwapPool(factory.createPool(address(poolToken))); poolToken.mint(address(this), uint256(STARTING_X)); weth.mint(address(this), uint256(STARTING_Y)); poolToken.approve(address(pool), type(uint256).max); weth.approve(address(pool), type(uint256).max); // Deposit Into Pool pool.deposit(uint256(STARTING_Y), uint256(STARTING_Y), uint256(STARTING_X), uint64(block.timestamp)); handler = new Handler(pool); bytes4[] memory selectors = new bytes4[](2); selectors[0] = handler.deposit.selector; selectors[1] = handler.swapPoolTokenForWethBasedOnOutputWeth.selector; targetSelector(FuzzSelector({ addr: address(handler), selectors: selectors })); targetContract(address(handler)); } function statefulFuzz_constantProductFormulaStaysTheSameY() public { assertEq(handler.actualDeltaY(), handler.expectedDeltaY()); } } ```