import {ArbitrumTest} from "foundry-arbitrum/ArbitrumTest.sol";

import {L1Contract} from "../src/L1Contract.sol";
import {L2Contract} from "../src/L2Contract.sol";

contract ExampleTest is Test, ArbitrumTest {
    L1Contract l1Contract;
    L2Contract l2Contract;

    function setUp() public {
        // Our L2 contract that will communicate with the L1 contract
        // via ArbSys precompile at address(0x64) (mocked and etched in ArbitrumTest)
        l2Contract = new L2Contract();

        // Our L1 contract that will communicate with the L2 contract
        // via inbox (mock deployed in ArbitrumTest)
        l1Contract = new L1Contract(address(inbox), address(l2Contract));

        l2Contract.setL1Target(address(l1Contract));
    }

    function testMessage() public {
        // assert how *succesful* cross-chain messages would modify state
        // (using the mocks implies that cross-chain messages are atomic & successful)
    }
}

import {IInbox} from "@arbitrum/nitro-contracts/src/bridge/IInbox.sol";

// Arbitrum Inbox (message handler)
IInbox public inbox;

constructor(address _inbox, address _l2Target) {
    inbox = IInbox(_inbox);
    l2Target = _l2Target;
}

...

// calls `handleMessageFromL1(uint256 num)` on L2
bytes memory data = abi.encodeWithSelector(L2Contract.handleMessageFromL1.selector, number);

inbox.createRetryableTicket{value: msg.value}(
    l2Target, 0, maxSubmissionCost, msg.sender, msg.sender, maxGas, gasPriceBid, data
);

import {IArbSys} from "./interfaces/IArbSys.sol";

// canonical precompile used to send messages to L1
IArbSys constant arbsys = IArbSys(address(0x0000000000000000000000000000000000000064));

...

// calls `handleMessageFromL2(uint256 num)` on L1
bytes memory data = abi.encodeWithSelector(L1Contract.handleMessageFromL2.selector, number);
arbsys.sendTxToL1(l1Target, data);