testing-patterns

Foundry MCP Testing Patterns & Infrastructure

Overview

This project uses a modern, reliable testing approach with assert_fs + temp-env that provides perfect isolation and real filesystem operations. The old trait-based mocking approach was replaced due to "leaky abstractions" and complexity.

Core Testing Philosophy

Why This Approach Won:

• Real Operations: Tests use actual filesystem calls, matching production exactly
• Perfect Isolation: Each test gets unique temporary environment with automatic cleanup
• No Mocking Complexity: Eliminates fragile trait hierarchies and dependency injection
• Production Fidelity: Tests catch real bugs that mocked tests might miss

TestEnvironment Pattern

Basic Structure

#[test]
fn test_name() {
    use crate::test_utils::TestEnvironment;
    let env = TestEnvironment::new().unwrap();

    let _ = env.with_env_async(|| async {
        // Test logic with real filesystem operations
        // Full environment isolation guaranteed
    });
}

Key Components

• TestEnvironment: Manages temporary directories and environment variables
• with_env_async: Bridges sync temp-env with async test execution
• assert_fs::TempDir: Automatic cleanup and cross-platform support
• temp-env: Scoped environment variable management

Environment Isolation

How It Works

// Each test gets isolated environment:
// - HOME = temp directory
// - CURSOR_CONFIG_DIR = temp/.cursor
// - CLAUDE_CONFIG_DIR = temp/.claude
// - Foundry specs = temp/.foundry

env.with_env_async(|| async {
    // Test runs in completely isolated environment
    // No risk of polluting user's real ~/.foundry
});

Benefits

• Parallel Execution: Tests can run simultaneously without interference
• Panic Safety: Environment restored even if tests panic
• Automatic Cleanup: No manual teardown required
• Cross-Platform: Works consistently across macOS, Linux, Windows

Helper Methods