## How to Simulate a Uniswap V2 Swap In this lesson, we will learn how to simulate a swap on Uniswap V2. To do this, we will use Foundry. ### Prerequisites * You should have a FORK_URL set up for your environment. You can get this from a service like Alchemy. * You should have the UniswapV2 contracts deployed in your environment. ### Simulating a Swap We will be testing the `swapTokensForExactTokens` function. ```solidity // Receive an exact amount of output tokens for as few input tokens // as possible function test_swapTokensForExactTokens() public { address[] memory path = new address[](3); path[0] = WETH; path[1] = DAI; path[2] = MKR; uint256 amountOut = 0.1 * 1e18; // 1e17 uint256 amountInMax = 1e18; vm.prank(user); // Input token amount and all subsequent output token amounts uint256[] memory amounts = router.swapTokensForExactTokens({ amountOut: amountOut, amountInMax: amountInMax, path: path, to: user, deadline: block.timestamp }); console2.log("WETH: %18e", amounts[0]); console2.log("DAI: %18e", amounts[1]); console2.log("MKR: %18e", amounts[2]); assertEq(mkr.balanceOf(user), amountOut, "MKR balance of user"); } ``` ### Running the Test We'll run the test with the following command: ```bash forge test --fork-url $FORK_URL --mp test/uniswap-v2/exercises/UniswapV2Swap.test.sol --mt test_swapTokensForExactTokens -vvv ``` ### The Test Results The test results will include logs. Inside the logs you will see that we had 1 WETH initially, but our test used a smaller amount of WETH. We also confirmed that we received 0.1 MKR.