swift-testing

A set of guidelines for writing and reviewing tests in Swift, Apple's programming language. Swift Testing is Apple's modern testing system, while XCTest is its older testing framework.

In plain words
What is it for?
Use it to create or review unit and integration tests, asynchronous tests, network mocks, confirmations, time limits, and migrations from XCTest.
Why use it?
It helps tests check the intended behavior clearly and use current Swift concurrency and testing features.

Skill for Claude CodeCodex

Install

Getting it into your agent

One page per mod, every tool's command on it. A separate URL per tool would split the same page into five that compete with each other.

agentmods
npx agentmods add skills/fiveonecode/agent-skills/swift-testing
Any agent
npx skills add fiveonecode/agent-skills --skill swift-testing
Clone the repo
git clone --depth 1 https://github.com/fiveonecode/agent-skills

Made for: Claude Code, Codex.

Per session 66 Skills are progressive disclosure: only the name and description are preloaded; the body loads when the skill is used.
When invoked 1,218 The whole file, excluding the scripts and references it only reads on demand.
Security scan A 0 findings. Scan, not verified.
Origin 86% copy Near-identical to another mod in the catalogue.
Token cost

What it costs to keep this loaded

Counted locally with the o200k_base tokenizer, which is exact for GPT models; Claude uses its own tokenizer and its counts differ. Treat this as one consistent yardstick across the catalogue rather than a bill. Prices are per million input tokens.

ModelPer sessionOnce invoked
Fable 5 $0.00066 $0.01218
Opus 5 $0.00033 $0.00609
Sonnet 5 $0.00013 $0.00244
Haiku 4.5 $0.00007 $0.00122

Measured yesterday against content hash 31e33269b014, method: parsed. Prices are Anthropic first-party input rates as of 2026-08-30, from the pricing page.

Security

Grade A, and why

swift-testing scanned grade A with 0 findings against 26 rules in 11 categories — prompt injection, anti-refusal, data exfiltration, privilege escalation, supply chain, agent snooping, system-prompt leakage, SSRF and excessive agency — measured yesterday.

A static scan of the body, not an audit. Every finding is printed with the line that produced it so you can judge whether it matters here. A mod is markdown that instructs an agent; that is exactly why what it instructs is worth reading.

Nothing flagged

None of the 26 patterns this scan looks for appear in this file: no shell pipes, no recursive deletes, no credential paths, no hidden text, no instruction-override or anti-refusal phrasing, no agent-config snooping. That is not a guarantee, it is the absence of the things that are checkable.

Origin

This is a copy

86% identical to swift-testing-pro — 24 lines differ, which has more behind it and is treated as the original. This page carries a canonical link to it rather than competing with it.

swift-testing/SKILL.md · 110 lines

How it starts

The opening of the file, as written. The whole thing — 110 lines — stays where its author put it; the contents beside it link to each section on GitHub.

Write and review Swift Testing code for correctness, modern API usage, and adherence to project conventions. Report only genuine problems - do not nitpick or invent issues.

Review process:

  1. Ensure tests follow core Swift Testing conventions using references/core-rules.md.
  2. Validate test structure, assertions, dependency injection, and other best practices using references/writing-better-tests.md.
  3. Check async tests, confirmations, time limits, actor isolation, and networking mocks using references/async-tests.md.
  4. Ensure new features like raw identifiers, test scopes, exit tests, and attachments are used correctly using references/new-features.md.
  5. If migrating from XCTest, follow the conversion guidance in references/migrating-from-xctest.md.
  6. Check oracle strength: the test must prove the intended behavior, not merely exercise a path or accept broad normalized output.

If doing partial work, load only the relevant reference files.

Core Instructions

  • Target Swift 6.2 or later, using modern Swift concurrency.
  • As a Swift Testing developer, the user wants all new unit and integration tests to be written using Swift Testing, and they may ask for help migrating existing XCTest code to Swift Testing.
  • Swift Testing does not support UI tests – XCTest must be used there.
  • Use a consistent project structure, with folder layout determined by app features.
  • Treat weak or vacuous assertions as correctness issues, even when the test uses the right Swift Testing APIs.

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.

Read the full file on GitHub · 110 lines

Files

What ships with it

8 files beside SKILL.md in the same directory: the scripts, references and assets a skill reads on demand. Not counted in the per-session cost; read them before you install if any of them is executable.

Changes

What this file has done since we first saw it

Hashed on every crawl. A supply-chain change to an agent config is a question of when, not whether, so the history is kept rather than the latest state alone.

  1. yesterday First seen · 110 lines · 66 tokens per session scan A 31e33269b014

Subscribe to this mod's changes

swift-testing is a skill published in the GitHub repository fiveonecode/agent-skills (19 stars, last pushed 10d ago), licensed MIT. It adds 66 tokens to every session and 1,218 once invoked, about $0.0003 per session on Opus 5. A static security scan graded it A with 0 findings. It is 86% identical to swift-testing-pro, differing in 24 lines, and is treated as a copy.

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