feat: Try upgradeTo for testing

Author: fusmanii

contracts/SpokePool.sol

@@ -289,6 +289,18 @@ abstract contract SpokePool is
     // Allows cross domain admin to upgrade UUPS proxy implementation.
     function _authorizeUpgrade(address newImplementation) internal override onlyAdmin {}
 
+    /**
+     * @notice Try to upgrade to new implementation and then downgrade to old implementation.
+     * @dev This is used to test the upgradeability of the contract.
+     * @param newImplementation New implementation address.
+     */
+    function try_upgradeTo(address newImplementation) public {
+        address oldImplementation = _getImplementation();
+        upgradeTo(newImplementation);
+        upgradeTo(oldImplementation);
+        revert("SUCCESSFULLY_UPGRADED_AND_DOWNGRADED");
+    }
+
     /**
      * @notice Pauses deposit-related functions. This is intended to be used if this contract is deprecated or when
      * something goes awry.