What problem does it solve?
Swift code that directly accesses external dependencies like file systems, networks, or cloud APIs is difficult to test, as it requires real I/O operations and makes it impossible to reliably test error handling paths or cross-environment behavior without unwanted side effects.
Core Features & Use Cases
- Protocol Abstraction: Define small, focused protocols for each external concern (file system, network, iCloud) to decouple implementation from business logic.
- Testable Implementations: Create production default implementations and configurable mock implementations for testing error scenarios without real I/O.
- Cross-Environment Compatibility: Write code that works seamlessly across app, test, and SwiftUI preview contexts using dependency injection with default parameters.
- Use Case: A Swift app that syncs user data to iCloud can use these patterns to test sync failures, missing container errors, and data read/write issues without touching real iCloud storage or the local file system.
Quick Start
Use this skill to refactor your Swift data sync manager to use protocol-based dependencies for deterministic testing of error paths without real I/O.
