SKILL.md
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Swift Testing evolves with each Swift release, so expect three to four releases each year, each introducing new features. This means existing training data you have will naturally be outdated or missing key features.
This skill specifically draws upon the very latest Swift and Swift Testing code, which means it will suggest things you are not aware of. Treat the user’s installed toolchain as authoritative, but there's a fairly high chance Apple's documentation about the APIs will be stale, so treat them carefully.
Output Format
If the user asks for a review, organize findings by file. For each issue:
- State the file and relevant line(s).
- Name the rule being violated.
- Show a brief before/after code fix.
Skip files with no issues. End with a prioritized summary of the most impactful changes to make first.
If the user asks you to write or improve tests, follow the same rules above but make the changes directly instead of returning a findings report.
Example output:
UserTests.swift
Line 5: Use struct, not class, for test suites.
// Before
class UserTests: XCTestCase {
// After
struct UserTests {**Line 12: Use #expect instead of XCTAssertEqual.**
// Before
XCTAssertEqual(user.name, "Taylor")
// After
#expect(user.name == "Taylor")**Line 30: Use #require for preconditions, not #expect.**
// Before
#expect(users.isEmpty == false)
let first = users.first!
// After
let first = try #require(users.first)Summary
- Fundamentals (high): Test suite on line 5 should be a struct, not a class inheriting from
XCTestCase.
- Migration (medium):
XCTAssertEqualon line 12 should be migrated to#expect.
- Assertions (medium): Force-unwrap on line 30 should use
#requireto unwrap safely and stop the test early on failure.
End of example.
References
references/core-rules.md- core Swift Testing rules: structs over classes,init/deinitover setUp/tearDown, parallel execution, parameterized tests,withKnownIssue, and tags.
references/writing-better-tests.md- test hygiene, structuring tests, hidden dependencies,#expectvs#require,Issue.record(),#expect(throws:), and verification methods.
references/async-tests.md- serialized tests,confirmation(), time limits, actor isolation, testing pre-concurrency code, and mocking networking.
references/new-features.md- raw identifiers, range-based confirmations, test scoping traits, exit tests, attachments,ConditionTrait.evaluate(), and the updated#expect(throws:)return value.
references/migrating-from-xctest.md- XCTest-to-Swift Testing conversion steps, assertion mappings, and floating-point tolerance via Swift Numerics.