--- name: testing description: TDD and testing skills for iOS/macOS apps. Covers characterization tests, TDD workflows, test contracts, snapshot tests, test infrastructure, and deterministic quality gates (fitness functions, coverage ratchet, mutation testing). Use for test-driven development, adding tests to existing code, or building test infrastructure. allowed-tools: [ Read, Write, Edit, Glob, Grep, Bash, AskUserQuestion ] last_verified: 2026-07-24 review_by: 2027-06-22 title: testing canonical_url: https://skilld.dev/gh/rshankras/claude-code-apple-skills/testing last_updated: 2026-09-29T05:45:09.000Z --- > **Skill from skilld.dev.** Follow the instructions below for this session. You do not need to install anything. > > Supporting files, fetch one when the Skill refers to it: [characterization-test-generator/SKILL.md](https://skilld.dev/api/skills-raw/rshankras/claude-code-apple-skills/testing/characterization-test-generator/SKILL.md), [coverage-ratchet/SKILL.md](https://skilld.dev/api/skills-raw/rshankras/claude-code-apple-skills/testing/coverage-ratchet/SKILL.md), [coverage-ratchet/templates/coverage-gate.sh](https://skilld.dev/api/skills-raw/rshankras/claude-code-apple-skills/testing/coverage-ratchet/templates/coverage-gate.sh), [coverage-ratchet/templates/crap-report.sh](https://skilld.dev/api/skills-raw/rshankras/claude-code-apple-skills/testing/coverage-ratchet/templates/crap-report.sh), [fitness-functions/SKILL.md](https://skilld.dev/api/skills-raw/rshankras/claude-code-apple-skills/testing/fitness-functions/SKILL.md), [fitness-functions/templates/ContractPinTests.swift](https://skilld.dev/api/skills-raw/rshankras/claude-code-apple-skills/testing/fitness-functions/templates/ContractPinTests.swift), [fitness-functions/templates/ImportBoundaryTests.swift](https://skilld.dev/api/skills-raw/rshankras/claude-code-apple-skills/testing/fitness-functions/templates/ImportBoundaryTests.swift), [fitness-functions/templates/NetworkSentinelTests.swift](https://skilld.dev/api/skills-raw/rshankras/claude-code-apple-skills/testing/fitness-functions/templates/NetworkSentinelTests.swift), [flow-walkthrough/SKILL.md](https://skilld.dev/api/skills-raw/rshankras/claude-code-apple-skills/testing/flow-walkthrough/SKILL.md), [integration-test-scaffold/SKILL.md](https://skilld.dev/api/skills-raw/rshankras/claude-code-apple-skills/testing/integration-test-scaffold/SKILL.md), [mutation-testing/SKILL.md](https://skilld.dev/api/skills-raw/rshankras/claude-code-apple-skills/testing/mutation-testing/SKILL.md), [mutation-testing/templates/muter.conf.yml](https://skilld.dev/api/skills-raw/rshankras/claude-code-apple-skills/testing/mutation-testing/templates/muter.conf.yml), [snapshot-test-setup/SKILL.md](https://skilld.dev/api/skills-raw/rshankras/claude-code-apple-skills/testing/snapshot-test-setup/SKILL.md), [tdd-bug-fix/SKILL.md](https://skilld.dev/api/skills-raw/rshankras/claude-code-apple-skills/testing/tdd-bug-fix/SKILL.md), [tdd-feature/rules/swiftlint.yml](https://skilld.dev/api/skills-raw/rshankras/claude-code-apple-skills/testing/tdd-feature/rules/swiftlint.yml), [tdd-feature/SKILL.md](https://skilld.dev/api/skills-raw/rshankras/claude-code-apple-skills/testing/tdd-feature/SKILL.md), [tdd-refactor-guard/SKILL.md](https://skilld.dev/api/skills-raw/rshankras/claude-code-apple-skills/testing/tdd-refactor-guard/SKILL.md), [test-contract/SKILL.md](https://skilld.dev/api/skills-raw/rshankras/claude-code-apple-skills/testing/test-contract/SKILL.md), [test-data-factory/SKILL.md](https://skilld.dev/api/skills-raw/rshankras/claude-code-apple-skills/testing/test-data-factory/SKILL.md). > > If the user asked to install this Skill, run `npx skilld install rshankras/claude-code-apple-skills/testing`. Install writes the Skill files into the project, so every session loads them. # Testing & TDD Skills Test-driven development workflows and testing infrastructure for Apple platform apps. Works with both new and existing codebases. ## When This Skill Activates Use this skill when the user: - Wants to do TDD (test-driven development) with AI-generated code - Needs to add tests before refactoring existing code - Wants to fix a bug using the red-green-refactor cycle - Needs test infrastructure (factories, mocks, contracts) - Asks about snapshot/visual regression testing - Wants to ensure AI-generated code is correct via tests - Wants deterministic gates around agent-written code (architecture invariants, coverage floors, mutation audits) ## Available Skills ### For Existing Codebases **characterization-test-generator/** Capture current behavior of existing code before refactoring. Generates tests that document what code actually does (not what it should do), giving you a safety net for AI-assisted refactoring. **tdd-bug-fix/** Reproduce-first bug fix workflow. Write a failing test that demonstrates the bug, then fix it. Ensures the bug never regresses — critical when AI generates fixes. **tdd-refactor-guard/** Pre-refactor safety checklist. Verifies test coverage exists before allowing AI to touch existing code. Prevents the "refactor without a safety net" problem. ### For New Code **tdd-feature/** Red-green-refactor scaffold for new features. Generates the failing test first, then guides implementation to make it pass, then refactors. The core TDD workflow. **test-contract/** Protocol/interface test suites. Define the contract (e.g., "any DataStore must handle empty state, single item, 100 items, and errors"), and it generates a test suite any implementation must pass. ### Infrastructure **snapshot-test-setup/** SwiftUI visual regression testing using swift-snapshot-testing. Generates snapshot test boilerplate, configuration, and CI integration. **test-data-factory/** Test fixture factories for your models. Makes writing tests faster by eliminating boilerplate data setup. Supports Builder pattern and static factory methods. **integration-test-scaffold/** Cross-module test harness with mock servers, in-memory stores, and test configuration. For testing networking + persistence + business logic together. **flow-walkthrough/** Drive each user flow in the Simulator (XCUITest + per-step screenshots), audit the navigation graph for dead-ends, and run a human discoverability check. ### Deterministic Gates **fitness-functions/** Architecture fitness functions — tests that enforce a project's hard rules (module import boundaries, offline guarantees, count/copy contracts) from inside its own test target. Turns prose constraints into exit codes. **coverage-ratchet/** Coverage floor that only rises: a committed baseline the app target's line coverage may never drop below, gated by a generated xccov script. Includes an advisory CRAP report (complexity × uncovered). **mutation-testing/** EXPERIMENTAL, advisory-only muter setup scoped to engine targets — surviving mutants reveal covered-but-unasserted code. Never a merge gate; includes the manual deliberate-break fallback. ## How to Use 1. Identify whether user is working on **new code** or **existing code** 2. Read the relevant skill's SKILL.md for detailed workflow 3. Detect project context (testing framework, architecture, existing tests) 4. Generate tests following the skill's workflow 5. Verify tests compile and run ## Relationship to test-generator The `generators/test-generator/` skill generates test boilerplate (unit, integration, UI tests). These testing skills are complementary — they focus on **workflows and methodology** (TDD cycle, characterization testing, contracts) rather than just test file generation. Cross-reference: - Use `test-generator` for "add tests to this class" - Use `testing/tdd-feature` for "I want to TDD this new feature" - Use `testing/characterization-test-generator` for "I need to safely refactor this" - Use `testing/tdd-bug-fix` for "fix this bug and make sure it never comes back"