added a mock gateway for upgrade

core/packages/contracts/test/GatewayUpgradeMock.sol

@@ -0,0 +1,33 @@
+// SPDX-License-Identifier: Apache-2.0
+// SPDX-FileCopyrightText: 2023 Snowfork <[email protected]>
+pragma solidity 0.8.20;
+
+import {Channel, InboundMessage, OperatingMode, ParaID, Config, Command} from "../src/Types.sol";
+import {IGateway} from "../src/interfaces/IGateway.sol";
+import {Verification} from "../src/Verification.sol";
+
+contract GatewayUpgradeMock is IGateway {
+    /**
+     * Getters
+     */
+
+    function operatingMode() external pure returns (OperatingMode) { return OperatingMode.Normal; }
+    function channelOperatingModeOf(ParaID) external pure returns (OperatingMode) { return OperatingMode.Normal; }
+    function channelFeeRewardOf(ParaID) external pure returns (uint256, uint256) { return (0, 0); }
+    function channelNoncesOf(ParaID) external pure returns (uint64, uint64) { return (0, 0); }
+    function agentOf(bytes32) external pure returns (address) { return address(0); }
+    function implementation() external pure returns (address) { return address(0); }
+
+    function submitInbound( InboundMessage calldata, bytes32[] calldata, Verification.Proof calldata) external {}
+
+    function registerToken(address) external payable {}
+    function sendToken(address, ParaID, bytes32, uint128) external payable{}
+    function sendToken(address, ParaID, address, uint128) external payable {}
+
+    event Initialized(uint d0, uint d1);
+    function initialize(bytes memory data) external {
+        // Just decode and exit
+        (uint d0, uint d1) = abi.decode(data, (uint, uint));
+        emit Initialized(d0, d1);
+    }
+}