rounding test case

Author: hoytech

src/MaglevEulerSwap.sol

@@ -33,7 +33,8 @@ contract MaglevEulerSwap is MaglevBase {
         _py = params.py;
         _cx = params.cx;
         _cy = params.cy;
-        _fee = Math.max(params.fee, 1.0000000000001e18); // minimum fee required to compensate for rounding
+        _fee = 1e18 + params.fee;
+        //_fee = Math.max(1e18 + params.fee, 1.0000000000001e18); // minimum fee required to compensate for rounding
     }
 
     // FIXME: how to charge fees?

test/EulerSwap.t.sol

@@ -13,12 +13,14 @@ import {MaglevEulerSwap as Maglev} from "../src/MaglevEulerSwap.sol";
 contract EulerSwapTest is MaglevTestBase {
     Maglev public maglev;
 
+    uint256 minFee = 0.0000000000001e18;
+
     function setUp() public virtual override {
         super.setUp();
 
         vm.prank(owner);
         maglev = new Maglev(
-            _getMaglevBaseParams(), Maglev.EulerSwapParams({px: 1e18, py: 1e18, cx: 0.4e18, cy: 0.85e18, fee: 0})
+            _getMaglevBaseParams(), Maglev.EulerSwapParams({px: 1e18, py: 1e18, cx: 0.4e18, cy: 0.85e18, fee: minFee})
         );
 
         vm.prank(holder);
@@ -67,7 +69,7 @@ contract EulerSwapTest is MaglevTestBase {
         int256 origNAV = getHolderNAV();
 
         vm.prank(owner);
-        maglev.setEulerSwapParams(Maglev.EulerSwapParams({px: px, py: py, cx: 0.4e18, cy: 0.85e18, fee: 0}));
+        maglev.setEulerSwapParams(Maglev.EulerSwapParams({px: px, py: py, cx: 0.4e18, cy: 0.85e18, fee: minFee}));
 
         uint256 amountIn = 1e18;
         uint256 amountOut = maglev.quoteExactInput(address(assetTST), address(assetTST2), amountIn);
@@ -120,7 +122,7 @@ contract EulerSwapTest is MaglevTestBase {
         oracle.setPrice(address(assetTST), unitOfAccount, price);
 
         vm.prank(owner);
-        maglev.setEulerSwapParams(Maglev.EulerSwapParams({px: px, py: py, cx: cx, cy: cy, fee: 0}));
+        maglev.setEulerSwapParams(Maglev.EulerSwapParams({px: px, py: py, cx: cx, cy: cy, fee: minFee}));
 
         int256 origNAV = getHolderNAV();
 
@@ -147,4 +149,19 @@ contract EulerSwapTest is MaglevTestBase {
 
         assertGe(getHolderNAV(), origNAV);
     }
+
+    function test_roundingFailure() public {
+        vm.skip(true);
+
+        vm.prank(owner);
+        maglev.setEulerSwapParams(Maglev.EulerSwapParams({px: 1e18, py: 1e18, cx: 0.4e18, cy: 0.85e18, fee: 0}));
+
+        uint256 amountIn = 1.4e18;
+        uint256 amountOut = maglev.quoteExactInput(address(assetTST), address(assetTST2), amountIn);
+
+        assetTST.mint(address(this), amountIn);
+        assetTST.transfer(address(maglev), amountIn);
+        maglev.swap(0, amountOut, address(this), "");
+        assertEq(assetTST2.balanceOf(address(this)), amountOut);
+    }
 }