Swift Testing

What it does

This skill enables AI agents to assist with writing and understanding Swift tests using the modern Swift Testing framework. It replaces Apple's XCTest framework with a macro-based approach that offers more concise syntax, improved asynchronous support, and parallel test execution by default. The skill helps developers transition from XCTest concepts and write effective unit tests for Swift projects.

When to use it

• When migrating existing XCTest codebases to the Swift Testing framework.
• For writing new Swift unit tests, particularly when needing concise syntax and async support.
• To understand test failures and debug issues within Swift testing workflows.
• When implementing parameterized tests with multiple input sets.

Key capabilities

• Assertion Macros: Uses #expect for soft assertions (continues on failure) and #require for hard preconditions (stops the test).
• Test Structure Support: Assists in creating test suites (@Suite) and individual tests (@Test).
• Assertion Conversion: Provides guidance on translating XCTest assertions to Swift Testing equivalents.
• Error Handling Tests: Supports testing for specific error types using #expect(throws: ...) syntax.
• Parameterized Tests: Facilitates the creation of parameterized tests with input data sets.
• Async Testing Support: Enables writing asynchronous tests using async/await.
• Confirmation Blocks: Assists in implementing callback confirmations within tests.
• Tagging: Supports test tagging for categorization and filtering (e.g., @Tag static var fast).

Example prompts

• "How do I write an assertion in Swift Testing to check if a variable is nil?"
• "Can you show me how to create a parameterized test using the Swift Testing framework?"
• "What's the difference between #expect and #require in Swift Testing?"

Tips & gotchas

• Prioritize #expect: Use #expect for most assertions; reserve #require for preconditions only. Overusing #require can mask other failures.
• State Isolation: Remember that each test gets a new instance of the system under test (SUT).
• Cartesian Product Awareness: When using parameterized tests, always use zip to combine input arrays; otherwise, you may unintentionally create a Cartesian product.