Resolve L-04 (2 of 2): Add minAssets to helper contract's redeem method

src/BrrETHRedeemHelper.sol

@@ -15,6 +15,8 @@ contract BrrETHRedeemHelper {
         IWETH(0x4200000000000000000000000000000000000006);
     IBrrETH public immutable brrETH;
 
+    error InsufficientAssetsRedeemed();
+
     receive() external payable {}
 
     constructor(address _brrETH) {
@@ -23,17 +25,22 @@ contract BrrETHRedeemHelper {
 
     /**
      * @notice Redeem brrETH for ETH.
-     * @param  shares  uint256  Amount of shares to redeem.
-     * @param  to      address  ETH recipient.
+     * @param  shares     uint256  Amount of shares to redeem.
+     * @param  to         address  ETH recipient.
+     * @param  minAssets  uint256  The minimum amount of assets that must be redeemed.
      */
-    function redeem(uint256 shares, address to) external {
+    function redeem(uint256 shares, address to, uint256 minAssets) external {
         // Requires approval from the caller to spend their brrETH balance.
         brrETH.redeem(shares, address(this), msg.sender);
 
         // Comet's alias for an "entire balance" is `type(uint256).max`.
         _COMET.withdraw(address(_WETH), type(uint256).max);
 
         _WETH.withdraw(_WETH.balanceOf(address(this)));
+
+        if (address(this).balance < minAssets)
+            revert InsufficientAssetsRedeemed();
+
         to.safeTransferETH(address(this).balance);
     }
 }

test/BrrETHRedeemHelper.t.sol

@@ -26,18 +26,31 @@ contract BrrETHRedeemHelperTest is Test, Helper {
                              redeem
     //////////////////////////////////////////////////////////////*/
 
+    function testCannotRedeemInsufficientAssetsRedeemed() external {
+        uint256 shares = vault.deposit{value: 1 ether}(address(this), 1);
+
+        // An amount of assets which will be 1 wei greater than the actual amount of assets
+        // redeemed from brrETH shares (due to Comet rounding down).
+        uint256 assets = vault.convertToAssets(shares);
+
+        vm.expectRevert(BrrETHRedeemHelper.InsufficientAssetsRedeemed.selector);
+
+        redeemHelper.redeem(shares, address(this), assets);
+    }
+
     function testRedeem() external {
         uint256 shares = vault.deposit{value: 1 ether}(address(this), 1);
 
         // The amount of cWETH that will be redeemed from brrETH.
-        uint256 assets = vault.convertToAssets(shares);
+        uint256 assets = vault.convertToAssets(shares) -
+            _COMET_ROUNDING_ERROR_MARGIN;
 
         uint256 ethBalanceBefore = address(this).balance;
 
-        redeemHelper.redeem(shares, address(this));
+        redeemHelper.redeem(shares, address(this), assets);
 
         // Account for Comet rounding down and compare against the ETH amount received.
-        assertEq(assets - 1, address(this).balance - ethBalanceBefore);
+        assertLe(assets, address(this).balance - ethBalanceBefore);
 
         // The redeem helper should not maintain balances for any of the tokens it handles.
         assertEq(0, vault.balanceOf(address(redeemHelper)));
@@ -49,14 +62,15 @@ contract BrrETHRedeemHelperTest is Test, Helper {
     function testRedeemFuzz(uint8 ethMultiplier) external {
         uint256 msgValue = 1 ether * (uint256(ethMultiplier) + 1);
         uint256 shares = vault.deposit{value: msgValue}(address(this), 1);
-        uint256 assets = vault.convertToAssets(shares);
+        uint256 assets = vault.convertToAssets(shares) -
+            _COMET_ROUNDING_ERROR_MARGIN;
 
         uint256 ethBalanceBefore = address(this).balance;
 
-        redeemHelper.redeem(shares, address(this));
+        redeemHelper.redeem(shares, address(this), assets);
 
         // Account for Comet rounding down and compare against the ETH amount received.
-        assertLe(assets - 2, address(this).balance - ethBalanceBefore);
+        assertLe(assets, address(this).balance - ethBalanceBefore);
 
         assertEq(0, vault.balanceOf(address(redeemHelper)));
         assertEq(0, COMET.balanceOf(address(redeemHelper)));