test-contract_skill

Overview

This skill generates reusable contract test suites for Swift protocols so every implementation can be validated against the same behavioral specification. Define the protocol contract once and produce generic tests that concrete implementations (real, mock, or AI-generated) must pass. It helps prevent regressions when swapping data stores, network clients, caches, or auth backends.

How this skill works

The skill inspects a protocol signature and extracts required methods, properties, and invariants, then maps each element to clear behavioral assertions (success, failure modes, edge cases, and invariants). It emits a generic, parameterizable Swift test suite (async-safe) that can be instantiated per implementation or run parametrically across implementations. Tests include CRUD, error paths, ordering, thread-safety considerations, and explicit invariants like count consistency.

When to use it

• Designing a new protocol and needing a single source of truth for behavior
• You have multiple implementations (in-memory, DB, cloud, mock) and must ensure parity
• Swapping persistence layers (e.g., CoreData → SwiftData) or client implementations
• Validating AI-generated or third-party implementations against your spec
• Adding regression protection when evolving protocol contracts

Best practices

• Write clear, minimal protocol docs describing expected side effects and invariants before generating tests
• Cover success paths, common error cases, and boundary conditions for each method
• Keep contract tests implementation-agnostic: use factory closures to create instances
• Include invariants as explicit tests (e.g., count == fetchAll().count) and run them after mutations
• Run contract suites in CI for every implementation and fail builds on divergence

Example use cases

• Generate a DataStore contract suite covering save/fetch/delete/fetchAll and invariants, then run it against InMemory, SQLite, and Cloud stores
• Create a NetworkClient contract that asserts parsing, 4xx/5xx handling, timeout and retry behavior across mock and real clients
• Build a Cache contract testing TTL, eviction policy, persistence across init, and thread-safety for LRU and memory caches
• Validate an Authentication contract that checks login success, rejection of bad credentials, token refresh, and logout state clearing