Setup Swift Testing Framework and Create Comprehensive Testing Infrastructure

[Copilot]

This PR establishes a complete modern testing infrastructure for SwiftSupabaseSync using Swift's new testing framework introduced in Swift 6.0+. The implementation provides a systematic approach to testing the library's 58 Swift source files with prioritized coverage targets and comprehensive documentation.

Key Changes

Swift Testing Framework Integration

• Updated Package.swift to tools-version 6.0+ with Swift Testing dependency
• Converted existing XCTest-based tests to modern @Test attributes
• Implemented async/await support for testing modern Swift patterns
• Created foundational test structure in Tests/SwiftSupabaseSyncTests/CoreDomain/

Comprehensive Testing Documentation

Created three detailed guides:

1. Tests/README.md (8,311 characters) - Complete testing strategy with:

   • 3-tier priority system (Critical/Important/Supporting)
   • Coverage targets: 95%/85%/70% respectively
   • 4-phase implementation roadmap
   • Modern Swift Testing patterns and examples

2. MACOS_SETUP.md (7,367 characters) - Full macOS development environment setup covering:

   • System requirements and Xcode configuration
   • Swift Testing framework integration
   • IDE setup for Xcode and VS Code
   • CI/CD configuration with GitHub Actions
   • Local Supabase development setup

3. IMPLEMENTATION_SUMMARY.md (5,338 characters) - Technical implementation details and progress tracking

Foundation Test Implementation

Created SyncableTests demonstrating modern Swift Testing patterns:

@Test("Syncable entity should initialize with correct defaults")
func testBasicInitialization() async throws {
    let entity = MockSyncableEntity()
    #expect(!entity.isDeleted)
    #expect(entity.needsSync == true)
}

The tests cover core synchronization functionality including entity initialization, content hashing, sync state logic, and conflict resolution types.

Platform Compatibility Solutions

Addressed cross-platform development challenges by:

• Documenting platform-specific framework dependencies (Combine, Network, Security)
• Implementing conditional compilation strategies
• Creating protocol-based abstractions for testability

Testing Priority Structure

Tier 1 (Critical - 95% coverage): Core Domain entities, protocols, and use cases
Tier 2 (Important - 85% coverage): Data layer repositories and infrastructure
Tier 3 (Supporting - 70% coverage): Dependency injection and utility services

Benefits

1. Modern Testing Framework: Leverages Swift 6.0+ testing capabilities with better async support and cleaner syntax
2. Systematic Approach: Clear prioritization ensures critical business logic is thoroughly tested first
3. Complete Documentation: Developers have comprehensive guides for setup, testing patterns, and implementation
4. Foundation for Quality: Establishes infrastructure for maintaining high code quality as the library grows

This infrastructure enables systematic, test-driven development of SwiftSupabaseSync with modern Swift practices and comprehensive coverage tracking.

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