/testing

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

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"