new: fxBase for tests; mock state sender/receiver

contracts/mock/StateReceiver.sol

@@ -0,0 +1,18 @@
+// SPDX-License-Identifier: MIT
+pragma solidity ^0.8.0;
+
+interface IFxChild {
+    function onStateReceive(uint256 stateId, bytes calldata _data) external;
+}
+
+contract MockStateReceiver {
+    address public immutable fxChild;
+
+    constructor(address _fxChild) {
+        fxChild = _fxChild;
+    }
+
+    function receiveState(uint256 stateId, bytes calldata _data) external {
+        IFxChild(fxChild).onStateReceive(stateId, _data);
+    }
+}

contracts/mock/StateSender.sol

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+// SPDX-License-Identifier: MIT
+pragma solidity ^0.8.0;
+
+interface IStateReceiver {
+    function receiveState(uint256 stateId, bytes calldata data) external;
+
+    function fxChild() external returns (address);
+}
+
+contract MockStateSender {
+    event StateSynced(uint256 indexed id, address indexed contractAddress, bytes data);
+    IStateReceiver public stateReceiver;
+
+    constructor(address _stateReceiver) {
+        stateReceiver = IStateReceiver(_stateReceiver);
+    }
+
+    function updateStateReceiver(address _where) public {
+        stateReceiver = IStateReceiver(_where);
+    }
+
+    function syncState(address /*receiver*/, bytes calldata data) external {
+        uint256 stateId = 1;
+        stateReceiver.receiveState(stateId, data);
+        emit StateSynced(stateId, stateReceiver.fxChild(), data);
+    }
+}

test/utils/FxBase.sol

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+// SPDX-License-Identifier: MIT
+pragma solidity ^0.8.0;
+
+import "@utils/Test.sol";
+import {FxRoot} from "contracts/FxRoot.sol";
+import {FxChild} from "contracts/FxChild.sol";
+import {MockStateSender} from "contracts/mock/StateSender.sol";
+import {MockStateReceiver} from "contracts/mock/StateReceiver.sol";
+
+contract FxBase is Test {
+    FxRoot public fxRoot;
+    FxChild public fxChild;
+    MockStateSender public stateSender;
+    MockStateReceiver public stateReceiver;
+
+    address public MATIC = 0x0000000000000000000000000000000000001001;
+
+    function setUp() public virtual {
+        fxChild = new FxChild();
+
+        stateReceiver = new MockStateReceiver(address(fxChild));
+
+        vm.etch(MATIC, address(stateReceiver).code);
+
+        stateSender = new MockStateSender(MATIC);
+        fxRoot = new FxRoot(address(stateSender));
+
+        fxRoot.setFxChild(address(fxChild));
+        fxChild.setFxRoot(address(fxRoot));
+    }
+}
+
+contract MockMessageProcessor {
+    event MessageProcessed(uint256 indexed stateId, address rootMessageSender, bytes data);
+
+    function processMessageFromRoot(uint256 stateId, address rootMessageSender, bytes calldata data) public {
+        emit MessageProcessed(stateId, rootMessageSender, data);
+    }
+}