in fuzz tests, exercise quoteExactOutput() code path

Author: hoytech

test/Basic.t.sol

@@ -114,6 +114,10 @@ contract Basic is EulerSwapTestBase {
 
         t1.mint(address(this), amount);
         uint256 q = periphery.quoteExactInput(address(eulerSwap), address(t1), address(t2), amount);
+        {
+            uint256 qRev = periphery.quoteExactOutput(address(eulerSwap), address(t1), address(t2), q);
+            assertApproxEqAbs(amount, qRev, 200 + (MAX_QUOTE_ERROR + 1) * 2); // max 100:1 price differential, 2 swaps
+        }
 
         t1.transfer(address(eulerSwap), amount);
         if (dir) eulerSwap.swap(0, q, address(this), "");
@@ -122,6 +126,10 @@ contract Basic is EulerSwapTestBase {
 
         t2.mint(address(this), amount2);
         uint256 q2 = periphery.quoteExactInput(address(eulerSwap), address(t2), address(t1), amount2);
+        {
+            uint256 qRev = periphery.quoteExactOutput(address(eulerSwap), address(t2), address(t1), q2);
+            assertApproxEqAbs(amount2, qRev, 200 + (MAX_QUOTE_ERROR + 1) * 2);
+        }
 
         t2.transfer(address(eulerSwap), amount2);
         if (dir) eulerSwap.swap(q2, 0, address(this), "");

test/PreserveNav.t.sol

@@ -42,6 +42,10 @@ contract PreserveNav is EulerSwapTestBase {
             else (t1, t2) = (assetTST2, assetTST);
 
             uint256 q = periphery.quoteExactInput(address(eulerSwap), address(t1), address(t2), amount1);
+            {
+                uint256 qRev = periphery.quoteExactOutput(address(eulerSwap), address(t1), address(t2), q);
+                assertApproxEqAbs(amount1, qRev, (MAX_QUOTE_ERROR + 1) * 2);
+            }
 
             t1.mint(address(this), amount1);
             t1.transfer(address(eulerSwap), amount1);
@@ -66,6 +70,10 @@ contract PreserveNav is EulerSwapTestBase {
             else (t1, t2) = (assetTST2, assetTST);
 
             uint256 q = periphery.quoteExactInput(address(eulerSwap), address(t1), address(t2), amount2);
+            {
+                uint256 qRev = periphery.quoteExactOutput(address(eulerSwap), address(t1), address(t2), q);
+                assertApproxEqAbs(amount2, qRev, (MAX_QUOTE_ERROR + 1) * 2);
+            }
 
             t1.mint(address(this), amount2);
             t1.transfer(address(eulerSwap), amount2);