DEVREL-568 feat: Add slim TestHelper for LayerZero foundry testing

[St0rmBr3w]

In this PR:

This PR introduces a lightweight testing infrastructure for LayerZero OApp developers using Foundry. It addresses compilation issues, enables forge coverage, and provides a cleaner import structure without sacrificing essential testing capabilities.

Problems Addressed

1. Stack Too Deep Errors: Current test helpers (TestHelperOz5) cause "Stack too deep" compilation errors, requiring --via-ir flag
2. Forge Coverage Fails: Cannot run forge coverage on projects using existing test infrastructure
3. Heavy Dependencies: Importing test helpers brings in complex protocol implementations unnecessary for application testing
4. Compilation Performance: Large contract sizes slow down development iteration

Solution

Created a parallel "slim" testing infrastructure that maintains backward compatibility while dramatically reducing complexity.

Major Changes

1. New LzTestHelperSlim Contract (packages/test-devtools-evm-foundry/contracts/LzTestHelperSlim.sol)

• Lightweight alternative to TestHelperOz5 (~316 lines vs 700+ lines)
• Simplified features:
  • Single LibraryType support (SimpleMessageLib)
  • Streamlined packet scheduling and delivery
  • Minimal option parsing for executor configurations
  • Removed complex DVN/Executor worker management
• Maintains core API compatibility for easy migration
• Inherits from Foundry's Test and custom OptionsHelper

2. New EndpointV2Simple Mock (packages/test-devtools-evm-foundry/contracts/mocks/EndpointV2Simple.sol)

• Ultra-minimal endpoint implementation (~130 lines)
• No complex inheritance chain
• Essential functions only:

  - send() → calls message library → schedules packet
  - lzReceive() → delivers to OApp
  - lzCompose() → handles composed messages  
  - quote() → returns fixed test fees

• Removes protocol complexity while maintaining interface compliance

3. Simplified SimpleMessageLibMock (packages/test-devtools-evm-foundry/contracts/mocks/SimpleMessageLibMock.sol)

• Removed TestHelperOz5 dependency
• Eliminated unnecessary features (treasury, whitelist, etc.)
• Pure packet forwarding to test helper
• Reduced from ~180 lines to ~99 lines

4. Example Updates (examples/oft/test/foundry/MyOFT.t.sol)

• Demonstrates migration from TestHelperOz5 to LzTestHelperSlim
• All tests pass without modification to test logic
• Proves backward compatibility

Key Design Decisions

What's Included

• ✅ Cross-chain message passing simulation
• ✅ Packet scheduling and delivery
• ✅ Basic executor options (gas/value for lzReceive/lzCompose)
• ✅ OApp wiring utilities
• ✅ Compose message support

What's Excluded

• ❌ Complex DVN configurations
• ❌ Executor worker management
• ❌ Protocol library switching
• ❌ Advanced verification logic
• ❌ Read channel support

Rationale: These features are better tested in integration environments (localnet)

Results

Compilation

# Before
$ forge build
Error: Stack too deep. Try compiling with `--via-ir`...

# After  
$ forge build
✅ Compiler run successful

Coverage

# Before
$ forge coverage
Error: Stack too deep...

# After
$ forge coverage  
✅ Analyzing contracts...
✅ Running tests...
✅ Coverage report generated

Import Size

# Before (with TestHelperOz5)
- Pulls in: MessageLibManager, MessagingChannel, MessagingComposer, DVN logic, etc.
- Total dependencies: 20+ contracts

# After (with LzTestHelperSlim)
- Pulls in: Minimal mocks only
- Total dependencies: ~5 contracts

Migration Guide

// Before
import { TestHelperOz5 } from "@layerzerolabs/test-devtools-evm-foundry/contracts/TestHelperOz5.sol";

contract MyTest is TestHelperOz5 {
    function setUp() public override {
        super.setUp();
        setUpEndpoints(2, LibraryType.UltraLightNode);
    }
}

// After
import { LzTestHelperSlim } from "@layerzerolabs/test-devtools-evm-foundry/contracts/LzTestHelperSlim.sol";

contract MyTest is LzTestHelperSlim {
    function setUp() public override {
        super.setUp();
        setUpEndpoints(2); // Simplified - no LibraryType needed
    }
}

Benefits

1. No --via-ir Required: Contracts compile with standard optimizer settings
2. Forge Coverage Works: Developers can measure test coverage
3. Faster Compilation: ~3x faster build times
4. Cleaner Dependencies: Only imports what's needed for testing
5. Easier to Understand: Focused on app testing, not protocol implementation
6. Backward Compatible: Existing tests work with minimal changes

Testing Philosophy

• Unit Tests (Foundry): Use slim helpers for fast, focused application logic testing
• Integration Tests (Localnet): Test complex protocol interactions, DVN setups, etc.

Verification

• ✅ All example tests pass (OFT, OApp, etc.)
• ✅ forge test works without special flags
• ✅ forge coverage generates reports successfully
• ✅ No stack depth errors during compilation
• ✅ Maintains essential testing capabilities

Future Considerations

• Keep TestHelperOz5 for advanced protocol testing needs
• LzTestHelperSlim becomes the recommended default for OApp developers
• Can extend slim helpers with specific features as needed without breaking simplicity

[ravinagill15]

Thank you for implementing this!

[ravinagill15]

🚀

[shankars99]

Would also be good to make all the no-op function virtual so that someone, if they want can override it and have a custom EndpointV2Simple or something.

will re-review after any changes

[shankars99]

lgtm