contracts-bedrock: Initializable test

Test coverage of the L1 `Initializable` contracts to cover the
case of contracts being reinitialized. No contract should be able
to have `initialize()` called twice.

packages/contracts-bedrock/test/Initializable.t.sol

+// SPDX-License-Identifier: MIT
+pragma solidity 0.8.15;
+
+import { ERC721Bridge_Initializer } from "test/CommonTest.t.sol";
+import { console } from "forge-std/console.sol";
+import { CrossDomainMessenger } from "src/universal/CrossDomainMessenger.sol";
+import { L2OutputOracle } from "src/L1/L2OutputOracle.sol";
+import { SystemConfig } from "src/L1/SystemConfig.sol";
+import { ResourceMetering } from "src/L1/ResourceMetering.sol";
+import { OptimismPortal } from "src/L1/OptimismPortal.sol";
+
+/// @title Initializer_Test
+/// @dev Ensures that the `initialize()` function on contracts cannot be called more than
+///      once. This contract inherits from `ERC721Bridge_Initializer` because it is the
+///      deepest contract in the inheritance chain for setting up the system contracts.
+contract Initializer_Test is ERC721Bridge_Initializer {
+   function test_cannotReinitializeL1_succeeds() public {
+       vm.expectRevert("Initializable: contract is already initialized");
+       L1Messenger.initialize(OptimismPortal(payable(address(0))));
+
+       vm.expectRevert("Initializable: contract is already initialized");
+       L1Bridge.initialize(CrossDomainMessenger(address(0)));
+
+       vm.expectRevert("Initializable: contract is already initialized");
+       oracle.initialize(0, 0, address(0), address(0));
+
+       vm.expectRevert("Initializable: contract is already initialized");
+       op.initialize(L2OutputOracle(address(0)), address(0), SystemConfig(address(0)), false);
+
+       vm.expectRevert("Initializable: contract is already initialized");
+       systemConfig.initialize({
+            _owner: address(0xdEaD),
+            _overhead: 0,
+            _scalar: 0,
+            _batcherHash: bytes32(0),
+            _gasLimit: 1,
+            _unsafeBlockSigner: address(0),
+            _config: ResourceMetering.ResourceConfig({
+                maxResourceLimit: 1,
+                elasticityMultiplier: 1,
+                baseFeeMaxChangeDenominator: 2,
+                minimumBaseFee: 0,
+                systemTxMaxGas: 0,
+                maximumBaseFee: 0
+            }),
+            _startBlock: type(uint256).max,
+            _batchInbox: address(0),
+            _addresses: SystemConfig.Addresses({
+                l1CrossDomainMessenger: address(0),
+                l1ERC721Bridge: address(0),
+                l1StandardBridge: address(0),
+                l2OutputOracle: address(0),
+                optimismPortal: address(0),
+                optimismMintableERC20Factory: address(0)
+            })
+       });
+
+       vm.expectRevert("Initializable: contract is already initialized");
+       L1NFTBridge.initialize(CrossDomainMessenger(address(0)));
+   }
+}