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Agent skill

Swift Testing

by johnrogers in johnrogers/claude-swift-engineering

A skill your agent uses when writing tests with Swift Testing (@Test,

MITAuto-check passedMobile

Install Swift Testing

skills CLI
$ npx skills add johnrogers/claude-swift-engineering --skill swift-testing -a claude-code

Project install by default; add -g for ~/.claude/skills/.

GitHub CLI
$ gh skill install johnrogers/claude-swift-engineering swift-testing --agent claude-code

Project scope by default; add --scope user for a personal install. Needs GitHub CLI 2.90.0 or later (public preview).

Manual copy
$ git clone --depth 1 https://github.com/johnrogers/claude-swift-engineering.git skills-src && mkdir -p .claude/skills && cp -r skills-src/plugins/swift-engineering/skills/swift-testing .claude/skills/swift-testing && rm -rf skills-src

Use ~/.claude/skills/ instead of .claude/skills for a personal install. The folder must contain SKILL.md.

Claude Code skills documentation · loads skills from .claude/skills/

Facts

Skill name
swift-testing
GitHub stars
231
Token cost
~1.1k tokens
SKILL.md length
339 words
Files
1
Skills in repo
17
Repo updated
First seen
Licence
MIT

At a glance

A skill your agent uses when writing tests with Swift Testing (@Test,

  • Works in 4 steps: Overusing #require — Use #expect for… → Forgetting state isolation — Each test… → Accidental Cartesian product — Always… → …
  • Writing tests with Swift Testing (@Test
  • SKILL.md covers Overview, References, Core Concepts and Test Structure, plus 7 more sections
  • Instructions only: no scripts, shell commands, URLs or credentials in SKILL.md

What it does

Swift Testing is an agent skill from johnrogers/claude-swift-engineering. Use when writing tests with Swift Testing (@Test,

Its SKILL.md is about 1.1k tokens, which your agent loads only when the skill is triggered. It is a single SKILL.md file with no bundled scripts.

It sits in Mobile, covering iOS development. The repository describes itself as: A collection of agents and skills to aid in the planning, implementation, documentation and testing of Swift/TCA code. The licence is MIT.

When your agent uses it

  • Writing tests with Swift Testing (@Test
  • Tasks that involve iOS development

Example prompts

  • “/swift-testing”

Workflow steps

4 steps, taken from the first numbered list in SKILL.md.

  1. Overusing #require — Use #expect for most checks
  2. Forgetting state isolation — Each test gets a NEW instance
  3. Accidental Cartesian product — Always use zip for paired inputs
  4. Not using .serialized — Apply for thread-unsafe legacy tests

What it can do on your machine

Read from SKILL.md and the folder at commit 1dc2cf4. It shows what the files ask for, not the result of running them.

  • Tool permissions

    Pre-approves nothing: there is no allowed-tools line, so your agent's usual permission prompts apply.

    From allowed-tools in the SKILL.md frontmatter.

  • Runs code

    No scripts in the folder and no shell commands in SKILL.md (its code samples are swift).

    From the folder's file list and the shell code blocks in SKILL.md.

  • Network

    Links to these hosts (documentation or services it may open):

    • developer.apple.com
    • steipete.me

    From URLs in SKILL.md, links to its own repository left out.

  • Credentials

    Names no API keys, tokens, secrets or passwords.

    From names ending in _API_KEY, _TOKEN, _SECRET, _KEY or _PASSWORD in SKILL.md.

Context cost

Swift Testing loads about 1.1k tokens when it runs. Until then it costs about 16 tokens; SKILL.md has 339 words of instructions outside code blocks.

Always · name and description, kept in context so the agent knows when to use it
~16
When it runs · the whole SKILL.md, loaded when a task matches
~1.1k

Estimates: characters ÷ 4, the usual rule of thumb; real counts depend on the model's tokenizer. Scripts and assets cost tokens only if the agent reads them.

Safety

Auto-check passed

The automated check found no risky patterns in SKILL.md.

Automated static check — not a guarantee. Review scripts before installing. It scans the text of SKILL.md for risky patterns (piping downloads into a shell, reading credential files, hidden Unicode, destructive commands); files beside SKILL.md are not scanned.

SKILL.md

The full file from johnrogers/claude-swift-engineering at commit 1dc2cf4, republished under its MIT licence (© johnrogers). 339 words, ~1,107 tokens.

Download SKILL.mdSave it as .claude/skills/swift-testing/SKILL.md (or your agent's skills folder).
name
swift-testing
description
Use when writing tests with Swift Testing (@Test,

Swift Testing Framework

Modern testing with Swift Testing framework. No XCTest.

Overview

Swift Testing replaces XCTest with a modern macro-based approach that's more concise, has better async support, and runs tests in parallel by default. The core principle: if you learned XCTest, unlearn it—Swift Testing works differently.

References

Core Concepts

Assertions
MacroUse Case
#expect(expression)Soft check — continues on failure. Use for most assertions.
#require(expression)Hard check — stops test on failure. Use for preconditions only.
Optional Unwrapping
swift
let user = try #require(await fetchUser(id: "123"))
#expect(user.id == "123")

Test Structure

swift
import Testing
@testable import YourModule

@Suite
struct FeatureTests {
    let sut: FeatureType
    
    init() throws {
        sut = FeatureType()
    }
    
    @Test("Description of behavior")
    func testBehavior() {
        #expect(sut.someProperty == expected)
    }
}

Assertion Conversions

XCTestSwift Testing
XCTAssert(expr)#expect(expr)
XCTAssertEqual(a, b)#expect(a == b)
XCTAssertNil(a)#expect(a == nil)
XCTAssertNotNil(a)#expect(a != nil)
try XCTUnwrap(a)try #require(a)
XCTAssertThrowsError#expect(throws: ErrorType.self) { }
XCTAssertNoThrow#expect(throws: Never.self) { }

Error Testing

swift
#expect(throws: (any Error).self) { try riskyOperation() }
#expect(throws: NetworkError.self) { try fetch() }
#expect(throws: NetworkError.timeout) { try fetch() }
#expect(throws: Never.self) { try safeOperation() }

Parameterized Tests

swift
@Test("Validates inputs", arguments: zip(
    ["a", "b", "c"],
    [1, 2, 3]
))
func testInputs(input: String, expected: Int) {
    #expect(process(input) == expected)
}

Warning: Multiple collections WITHOUT zip creates Cartesian product.

Async Testing

swift
@Test func testAsync() async throws {
    let result = try await fetchData()
    #expect(!result.isEmpty)
}
Confirmations
swift
@Test func testCallback() async {
    await confirmation("callback received") { confirm in
        let sut = SomeType { confirm() }
        sut.triggerCallback()
    }
}

Tags

swift
extension Tag {
    @Tag static var fast: Self
    @Tag static var networking: Self
}

@Test(.tags(.fast, .networking))
func testNetworkCall() { }

Common Pitfalls

  1. Overusing #require — Use #expect for most checks
  2. Forgetting state isolation — Each test gets a NEW instance
  3. Accidental Cartesian product — Always use zip for paired inputs
  4. Not using .serialized — Apply for thread-unsafe legacy tests

Common Mistakes

  1. Overusing #require — #require is for preconditions only. Using it for normal assertions means the test stops at first failure instead of reporting all failures. Use #expect for assertions, #require only when subsequent assertions depend on the value.

  2. Cartesian product bugs — @Test(arguments: [a, b], [c, d]) creates 4 combinations, not 2. Always use zip to pair arguments correctly: arguments: zip([a, b], [c, d]).

  3. Forgetting state isolation — Swift Testing creates a new test instance per test method. BUT shared state between tests (static variables, singletons) still leak. Use dependency injection or clean up singletons between tests.

  4. Parallel test conflicts — Swift Testing runs tests in parallel by default. Tests touching shared files, databases, or singletons will interfere. Use .serialized or isolation strategies.

  5. Not using async naturally — Wrapping async operations in Task { } defeats the purpose. Use async/await directly in test function signature: @Test func testAsync() async throws { }.

  6. Confirmation misuse — confirmation is for verifying callbacks were called. Using it for assertions is wrong. Use #expect for assertions, confirmation for callback counts.

© johnrogers, MIT. Rendered from Markdown: HTML in the file is shown as text, images as links, and headings moved down two levels. Raw file

Files

Just SKILL.md in plugins/swift-engineering/skills/swift-testing of johnrogers/claude-swift-engineering.

Open the folder on GitHubat commit 1dc2cf4

Compare with similar skills

Swift Testing next to the 5 skills that share the most tags, products or categories with it. Stars are the repository's; “used in” counts other GitHub owners with a copy.

Swift Testing compared with similar skills
SkillStarsUsed inTokensAuto-checkLicenceRepo updated
Swift Testing this skilljohnrogers/claude-swift-engineering231—~1.1kAutomated safety check: PassMIT
Swiftui Protwostraws/SwiftUI-Agent-Skill5k2 repos~1kAutomated safety check: PassMIT
Swiftui UI PatternsAFK-surf/OpenBridge4304 repos~887Automated safety check: PassMIT
Swiftui Performance Auditharperreed/dotfiles3348 repos~1.4kAutomated safety check: PassNone
Swift Testing ExpertAvdLee/Swift-Testing-Agent-Skill4681 repos~1.2kAutomated safety check: PassMIT
Hig Project Contextraintree-technology/hig-doctor1425 repos~1.2kAutomated safety check: PassMIT

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Categories

Questions about Swift Testing

What does Swift Testing do?

A skill your agent uses when writing tests with Swift Testing (@Test,. Swift Testing is an agent skill from johnrogers/claude-swift-engineering.

When should I use Swift Testing?

Swift Testing fits situations like: writing tests with Swift Testing (@Test; tasks that involve iOS development.

How do I install Swift Testing in Claude Code?

Run `npx skills add johnrogers/claude-swift-engineering --skill swift-testing -a claude-code`. Or copy the skill folder (plugins/swift-engineering/skills/swift-testing in johnrogers/claude-swift-engineering) into .claude/skills/swift-testing in your project. Claude Code loads it when a task matches its description.

How do I install Swift Testing in Codex?

Run `npx skills add johnrogers/claude-swift-engineering --skill swift-testing -a codex`. Or copy the skill folder (plugins/swift-engineering/skills/swift-testing in johnrogers/claude-swift-engineering) into .agents/skills/swift-testing in your project. Codex loads it when a task matches its description.

Can I use Swift Testing in Cursor, Gemini CLI or GitHub Copilot?

Cursor, Gemini CLI, GitHub Copilot and OpenCode also load SKILL.md folders. With the skills CLI, run `npx skills add johnrogers/claude-swift-engineering --skill swift-testing -a cursor` (or -a gemini-cli, github-copilot or opencode for the others). To copy it by hand, put the folder in .cursor/skills/swift-testing, .gemini/skills/swift-testing, .github/skills/swift-testing and .opencode/skills/swift-testing in your project.

What does Swift Testing need to run?

SKILL.md names no scripts, command-line tools or credentials: Swift Testing is instructions for the agent only.

Does Swift Testing access the network?

SKILL.md names 2 domains. As links in the text: developer.apple.com and steipete.me. This is read from the text; nothing was executed.

Is Swift Testing safe to install?

Our automated static check of SKILL.md found no risky patterns, such as piping downloads into a shell, reading credential files or hidden Unicode. It is not a guarantee. Review the folder before installing.

What licence does Swift Testing use?

Swift Testing is published under the MIT licence (the repository's licence). It allows redistribution, so the full SKILL.md is shown on this page.

How many tokens does Swift Testing use?

About 1.1k tokens (SKILL.md is roughly 4.4k characters). Agents keep only the skill's name and description in context until a task matches; then they load SKILL.md in full.

What are the alternatives to Swift Testing?

Skills that share tags, products or a category with Swift Testing: Swiftui Pro (twostraws/SwiftUI-Agent-Skill, 5k stars), Swiftui UI Patterns (AFK-surf/OpenBridge, 430 stars), Swiftui Performance Audit (harperreed/dotfiles, 334 stars) and Swift Testing Expert (AvdLee/Swift-Testing-Agent-Skill, 468 stars). The comparison table on this page puts their stars, adoption, token cost, safety result and licence side by side.

Who maintains Swift Testing?

johnrogers (a GitHub user) maintains it in johnrogers/claude-swift-engineering, which has 231 GitHub stars. The repository holds 17 skills in this directory. The repository was last updated on January 18, 2026.

Source: johnrogers/claude-swift-engineering on GitHub. Facts on this page come from the repository at the commit we read; the author's words are quoted as theirs.