test(ctb): Test that xdm v0 hashing matches legacy

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

@@ -5,6 +5,7 @@ import { CommonTest } from "./CommonTest.t.sol";
 import { Types } from "../libraries/Types.sol";
 import { Hashing } from "../libraries/Hashing.sol";
 import { Encoding } from "../libraries/Encoding.sol";
+import { LegacyCrossDomainUtils } from "../libraries/LegacyCrossDomainUtils.sol";
 
 contract Hashing_hashDepositSource_Test is CommonTest {
     /**
@@ -43,6 +44,28 @@ contract Hashing_hashCrossDomainMessage_Test is CommonTest {
             ffi.hashCrossDomainMessage(nonce, _sender, _target, _value, _gasLimit, _data)
         );
     }
+
+    /**
+     * @notice Tests that hashCrossDomainMessageV0 matches the hash of the legacy encoding.
+     */
+    function testFuzz_hashCrossDomainMessageV0_matchesLegacy_succeeds(
+        address _target,
+        address _sender,
+        bytes memory _message,
+        uint256 _messageNonce
+    ) external {
+        assertEq(
+            keccak256(
+                LegacyCrossDomainUtils.encodeXDomainCalldata(
+                    _target,
+                    _sender,
+                    _message,
+                    _messageNonce
+                )
+            ),
+            Hashing.hashCrossDomainMessageV0(_target, _sender, _message, _messageNonce)
+        );
+    }
 }
 
 contract Hashing_hashWithdrawal_Test is CommonTest {