import Math#average implementation from OZ, add additional test case

Author: ItsNickBarry

contracts/utils/Math.sol

@@ -11,7 +11,7 @@ library Math {
      */
     function average(uint256 a, uint256 b) internal pure returns (uint256) {
         unchecked {
-            return (a >> 1) + (b >> 1) + (a & b & 1);
+            return (a & b) + ((a ^ b) >> 1);
         }
     }
 

test/utils/Math.ts

@@ -40,6 +40,13 @@ describe('Math', function () {
             ethers.constants.MaxUint256,
           ),
         ).to.equal(ethers.constants.MaxUint256);
+
+        expect(
+          await instance.average(
+            ethers.constants.MaxUint256,
+            ethers.constants.MaxUint256.sub(ethers.constants.One),
+          ),
+        ).to.equal(ethers.constants.MaxUint256.sub(ethers.constants.One));
       });
     });