### Exercise 4 Solution: Remove All Liquidity In this lesson, we will learn to remove all liquidity, including fees, from a position by calling the `collect()` function. We will accomplish this by decreasing all liquidity for the position with a given `tokenId` and then transferring the tokens from the Nonfungible Position Manager to this contract by calling `collect()`. We will be using a function that we have previously written: ```javascript function test_decreaseLiquidity() public { uint256 tokenId = mint(); Position memory p0 = getPosition(tokenId); // Write your code here (uint256 amount0, uint256 amount1) = manager.decreaseLiquidity( INonfungiblePositionManager.DecreaseLiquidityParams({ tokenId: tokenId, liquidity: p0.liquidity, amount0Min: 0, amount1Min: 0, deadline: block.timestamp }) ); console2.log("Amount 0 decreased %e", amount0); console2.log("Amount 1 decreased %e", amount1); Position memory p1 = getPosition(tokenId); assertEq(p1.liquidity, 0); assertGt(p1.tokensOwed0, 0); assertGt(p1.tokensOwed1, 0); } ``` So let's start by copying that function into our current exercise. ```javascript function test_collect() public { uint256 tokenId = mint(); Position memory p0 = getPosition(tokenId); // Write your code here (uint256 amount0, uint256 amount1) = (0, 0); console2.log("--- collect ---"); console2.log("Amount 0 collected %e", amount0); console2.log("Amount 1 collected %e", amount1); Position memory p1 = getPosition(tokenId); assertEq(p1.liquidity, 0); assertEq(p1.tokensOwed0, 0); assertEq(p1.tokensOwed1, 0); } ``` First, we need to call `decreaseLiquidity()`. We'll copy over the code that calls it from the previous exercise. ```javascript (uint256 amount0, uint256 amount1) = manager.decreaseLiquidity( INonfungiblePositionManager.DecreaseLiquidityParams({ tokenId: tokenId, liquidity: p0.liquidity, amount0Min: 0, amount1Min: 0, deadline: block.timestamp }) ); ``` We do not need the output from this, so we can remove it from the variable declaration. ```javascript manager.decreaseLiquidity( INonfungiblePositionManager.DecreaseLiquidityParams({ tokenId: tokenId, liquidity: p0.liquidity, amount0Min: 0, amount1Min: 0, deadline: block.timestamp }) ); ``` Next, we must call the `collect()` function, but first, we have to determine what parameters to pass in, so we will open `INonfungiblePositionManager.sol` and look for the `collect` function parameters. Here we can see that we need to pass in a `CollectParams` struct, so we will copy the struct into our current exercise. ```javascript INonfungiblePositionManager.CollectParams({ uint256 tokenId; address recipient; uint128 amount0Max; uint128 amount1Max; }) ``` Before we can use this struct, we must declare the struct using the interface name: ```javascript (uint256 amount0, uint256 amount1) = manager.collect( INonfungiblePositionManager.CollectParams({ tokenId: tokenId, address recipient; uint128 amount0Max; uint128 amount1Max; }) ); ``` Now, let's populate the parameters. The `tokenId` will be the `tokenId` from the function. The `recipient` will be `address(this)`, which is the current contract. The maximum amount will be `type(uint128).max`. ```javascript (uint256 amount0, uint256 amount1) = manager.collect( INonfungiblePositionManager.CollectParams({ tokenId: tokenId, recipient: address(this), amount0Max: type(uint128).max, amount1Max: type(uint128).max }) ); ``` This completes the exercise for removing liquidity and collecting the tokens. Let's try running our test. ```bash forge test --fork-url $FORK_URL --match-path test/uniswap-v3/exercises/UniswapV3Liquidity.test.sol --match-test test_collect -vvv ``` The test passed!