get the totalAssets at a timestamp

contracts/test/MockERC4626.sol

@@ -153,6 +153,10 @@ contract MockERC4626 is ERC4626, MultiRolesAuthority {
         return asset.balanceOf(address(this)) + _getAccruedInterest();
     }
 
+    function totalAssets(uint256 timestamp) public view returns (uint256) {
+        return asset.balanceOf(address(this)) + _getAccruedInterest(timestamp);
+    }
+
     /// Mock ///
 
     function setMaxMintAmount(
@@ -207,4 +211,27 @@ contract MockERC4626 is ERC4626, MultiRolesAuthority {
         );
         return accrued;
     }
+
+    function _getAccruedInterest(
+        uint256 timestamp
+    ) internal view returns (uint256) {
+        // If the rate is zero, no interest has accrued.
+        if (_rate == 0) {
+            return 0;
+        }
+
+        // If the block timestamp is less than last updated, the accrual
+        // calculation will underflow. This can occur when using anvil's state
+        // snapshots.
+        if (block.timestamp < _lastUpdated) {
+            return 0;
+        }
+
+        // base_balance = base_balance * (1 + r * t)
+        uint256 timeElapsed = (timestamp - _lastUpdated).divDown(365 days);
+        uint256 accrued = asset.balanceOf(address(this)).mulDown(
+            _rate.mulDown(timeElapsed)
+        );
+        return accrued;
+    }
 }