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Test Quality Analysis

Detect test smells, overmocking, flaky tests, and coverage issues. Analyze test effectiveness, maintainability, and reliability. Use when reviewing tests or improving test quality.

airag
By secondsky
17928Updated 1 day agoTypeScriptMIT

Skill Content

# Test Quality Analysis

Expert knowledge for analyzing and improving test quality - detecting test smells, overmocking, insufficient coverage, and testing anti-patterns.

## Core Dimensions

- **Correctness**: Tests verify the right behavior
- **Reliability**: Tests are deterministic, not flaky
- **Maintainability**: Tests are easy to understand
- **Performance**: Tests run quickly
- **Coverage**: Tests cover critical code paths
- **Isolation**: Tests don't depend on external state

## Test Smells

### Overmocking

**Problem**: Mocking too many dependencies makes tests fragile.

```typescript
// ❌ BAD: Overmocked
test('calculate total', () => {
  const mockAdd = vi.fn(() => 10)
  const mockMultiply = vi.fn(() => 20)
  // Testing implementation, not behavior
})

// ✅ GOOD: Mock only external dependencies
test('calculate order total', () => {
  const mockPricingAPI = vi.fn(() => ({ tax: 0.1 }))
  const total = calculateTotal(order, mockPricingAPI)
  expect(total).toBe(38)
})
```

**Detection**: More than 3-4 mocks, mocking pure functions, complex mock setup.

**Fix**: Mock only I/O boundaries (APIs, databases, filesystem).

### Fragile Tests

**Problem**: Tests break with unrelated code changes.

```typescript
// ❌ BAD: Tests implementation details
await page.locator('.form-container > div:nth-child(2) > button').click()

// ✅ GOOD: Semantic selector
await page.getByRole('button', { name: 'Submit' }).click()
```

### Flaky Tests

**Problem**: Tests pass or fail non-deterministically.

```typescript
// ❌ BAD: Race condition
test('loads data', async () => {
  fetchData()
  await new Promise(resolve => setTimeout(resolve, 1000))
  expect(data).toBeDefined()
})

// ✅ GOOD: Proper async handling
test('loads data', async () => {
  const data = await fetchData()
  expect(data).toBeDefined()
})
```

### Poor Assertions

```typescript
// ❌ BAD: Weak assertion
test('returns users', async () => {
  const users = await getUsers()
  expect(users).toBeDefined() // Too vague!
})

// ✅ GOOD: Strong, specific assertions
test('creates user with correct attributes', async () => {
  const user = await createUser({ name: 'John' })
  expect(user).toMatchObject({
    id: expect.any(Number),
    name: 'John',
  })
})
```

## Analysis Tools

```bash
# Vitest coverage (prefer bun)
bun test --coverage
open coverage/index.html

# Check thresholds
bun test --coverage --coverage.thresholds.lines=80

# pytest-cov (Python)
uv run pytest --cov --cov-report=html
open htmlcov/index.html
```

## Best Practices Checklist

### Unit Test Quality (FIRST)
- [ ] **Fast**: Tests run in milliseconds
- [ ] **Isolated**: No dependencies between tests
- [ ] **Repeatable**: Same results every time
- [ ] **Self-validating**: Clear pass/fail
- [ ] **Timely**: Written alongside code

### Mock Guidelines
- [ ] Mock only external dependencies
- [ ] Don't mock business logic or pure functions
- [ ] Use real implementations when possible
- [ ] Limit to 3-4 mocks per test maximum

### Coverage Goals
- [ ] 80%+ line coverage for business logic
- [ ] 100% for critical paths (auth, payment)
- [ ] All error paths tested
- [ ] Boundary conditions tested

### Test Structure (AAA Pattern)

```typescript
test('user registration', async () => {
  // Arrange
  const userData = { email: 'user@example.com' }

  // Act
  const user = await registerUser(userData)

  // Assert
  expect(user.email).toBe('user@example.com')
})
```

## Code Review Checklist

- [ ] Tests verify behavior, not implementation
- [ ] Assertions are specific and meaningful
- [ ] No flaky tests (timing, ordering issues)
- [ ] Proper async/await usage
- [ ] Test names clearly describe behavior
- [ ] Minimal code duplication
- [ ] Critical paths have tests
- [ ] Both happy path and error cases covered

## Common Anti-Patterns

### Testing Implementation Details

```typescript
// ❌ BAD
const spy = vi.spyOn(Math, 'sqrt')
calculateDistance()
expect(spy).toHaveBeenCalled() // Testing how, not what

// ✅ GOOD
const distance = calculateDistance({ x: 0, y: 0 }, { x: 3, y: 4 })
expect(distance).toBe(5) // Testing output
```

### Mocking Too Much

```typescript
// ❌ BAD
const mockAdd = vi.fn((a, b) => a + b)

// ✅ GOOD: Use real implementations
import { add } from './utils'
// Only mock external services
const mockPaymentGateway = vi.fn()
```

## See Also

- `vitest-testing` - TypeScript/JavaScript testing
- `playwright-testing` - E2E testing
- `mutation-testing` - Validate test effectiveness

How to use

  1. Copy the skill content above
  2. Create a .claude/skills directory in your project
  3. Save as .claude/skills/claude-skills-test-quality-analysis.md
  4. Use /claude-skills-test-quality-analysis in Claude Code to invoke this skill

README

View on GitHub

Claude Code Skills Collection

170 production-ready skills for Claude Code CLI

Version 3.3.1 | Last Updated: 2026-05-14

<div align="center">

🔌 Platform Support

This repository uses Claude Plugin Patterns — natively supported by:

PlatformStatusNotes
Claude Code✅ NativeFull marketplace support
Factory Droid✅ NativeFull marketplace support
</div> **For all other Platforms like opencode, codex and others, you can use https://github.com/enulus/OpenPackage **

A curated collection of battle-tested skills for building modern web applications with Cloudflare, AI integrations, React, Tailwind, and more.

PS: if skills.sh warns about any skill: Their scan process is a outdated LLM which flags newest versions pins (like in ZOD) as non existent and by that potentially malicous.

Quick Start

Marketplace Installation (Recommended)

# Add the marketplace
/plugin marketplace add https://github.com/secondsky/claude-skills

# Install individual skills as needed
/plugin install cloudflare-d1@claude-skills
/plugin install tailwind-v4-shadcn@claude-skills
/plugin install ai-sdk-core@claude-skills

See MARKETPLACE.md for complete catalog of all 170 skills.

Bulk Installation (Contributors)

# Clone the repository
git clone https://github.com/secondsky/claude-skills.git
cd claude-skills

# Install all 170 skills at once
./scripts/install-all.sh

# Or install individual skills
./scripts/install-skill.sh cloudflare-d1

Repository Structure

This repository contains 170 production-tested skills for Claude Code, each focused on a specific technology or capability.

Individual Skills: Each skill is a standalone unit with:

  • SKILL.md - Core knowledge and guidance
  • Templates - Working code examples
  • References - Extended documentation
  • Scripts - Helper utilities

Installation Options:

  1. Individual - Install only the skills you need via marketplace
  2. Bulk - Install all 170 skills using ./scripts/install-all.sh

Available Skills (170 Individual Skills)

Each skill is individually installable. Install only the skills you need.

Full Catalog: See MARKETPLACE.md for detailed listings.

Categories

CategorySkillsExamples
tooling29turborepo, plan-interview, code-review
frontend26nuxt-v4, nuxt-v5, tailwind-v4-shadcn, tanstack-query, nuxt-studio, maz-ui, threejs
cloudflare21cloudflare-d1, cloudflare-workers-ai, cloudflare-agents
ai20openai-agents, claude-api, ai-sdk-core
api16api-design-principles, graphql-implementation
web10hono-routing, firecrawl-scraper, web-performance
mobile7swift-best-practices, react-native-app, react-native-skills
database6drizzle-orm-d1, neon-vercel-postgres, supabase-postgres-best-practices
security6csrf-protection, access-control-rbac
auth4better-auth
testing4vitest-testing, playwright-testing
design4design-review, design-system-creation
woocommerce4woocommerce-backend-dev
cms4hugo, sveltia-cms, wordpress-plugin-core
architecture3microservices-patterns, architecture-patterns
data3sql-query-optimization, recommendation-engine
seo2seo-optimizer, seo-keyword-cluster-builder
documentation1technical-specification

How It Works

Auto-Discovery

Claude Code automatically checks ~/.claude/skills/ for relevant skills before planning tasks:

User: "Set up a Cloudflare Worker with D1 database"
           ↓
Claude: [Checks skills automatically]
           ↓
Claude: "Found cloudflare-d1 skills.
         These prevent 12 documented errors. Use them?"
           ↓
User: "Yes"
           ↓
Result: Production-ready setup, zero errors, ~65% token savings

Note: Due to token limits, not all skills may be visible at once. See ⚠️ Important: Token Limits below.

Skill Structure

Each skill includes:

skills/[skill-name]/
├── SKILL.md              # Complete documentation
├── .claude-plugin/
│   └── plugin.json       # Plugin metadata
├── templates/            # Ready-to-copy templates
├── scripts/              # Automation scripts
└── references/           # Extended documentation

Recent Additions

May 2026

Supply Chain Security (cross-cutting):

  • dependency-upgrade expanded with Socket CLI integration — proactive malicious package detection, typosquatting alerts, and CI/CD security gates. New 418-line reference guide, 2 GitHub Actions templates, and expanded supply chain security comparison (3 tools)
  • 31 skills now include "Secure Installation" guidance — contextually-tailored security sections across all high-risk skill categories (scaffolding, MCP/agent SDKs, multi-provider installs, Docker, CI/CD). Covers 8 Bun skills, 5 Nuxt skills, 6 Cloudflare skills, 4 AI/agent skills, and 8 frontend/tooling skills
  • Supply chain security is now a first-class cross-cutting concern woven into the skill collection — not a standalone topic

February - April 2026

Full-Stack Frameworks:

  • nuxt-v5 (v1.0.0) - Full Nuxt 5 support with 4 skills (core, data, server, production), 3 diagnostic agents, and interactive setup wizard
  • supabase-postgres-best-practices - 30 Postgres optimization rules from Supabase across 8 categories
  • threejs (v1.0.0) - 3D web graphics: scenes, geometries, shaders, animations, post-processing

Infrastructure:

  • JSON schema validation - Automated plugin.json validation with CI support
  • GitHub issue templates - Skill-specific issue templates for bug reports, feature requests, and submissions

Plugin Enhancements:

  • mutation-testing - Added Bun native runner support
  • dependency-upgrade - Added supply chain security content

December 2025 - January 2026

Frontend Expansion:

  • nuxt-studio (v1.0.0) - Visual CMS for Nuxt Content with live preview, OAuth auth, and R2 storage integration
  • maz-ui (v1.0.0) - 50+ Vue/Nuxt components with theming, i18n, form generation, and 14 composables

Developer Workflow:

  • plan-interview (v2.0.0) - Adaptive interview-driven spec generation with autonomous quality review
  • turborepo (v2.8.0) - Updated to official Vercel skill with enhanced monorepo build optimization

Mobile Development:

  • react-native-skills (v1.0.0) - React Native & Expo best practices with performance optimization patterns

Enhanced Authentication:

  • better-auth (v2.2.0) - Expanded to 18 framework integrations with 30+ authentication plugins

⚠️ Important: Token Limits

Skill Visibility Constraint

Claude Code has a 15,000 character limit for the total size of skill descriptions in the system prompt. This limit also applies to commands and agents.

What this means:

  • Not all 170 skills may be visible in Claude's context at once
  • Skills are loaded based on relevance and available token budget
  • You can verify how many skills Claude currently sees by asking: "How many skills do you see in your system prompt?"

Checking Visible Skills

To verify which skills are currently loaded:

# Ask Claude Code directly
"Check what skills/plugins you see in your system prompt"

Claude will report something like: "85 of 170 skills visible due to token limits"

Workaround: Increase Token Budget

You can double the headroom for skill descriptions by setting an environment variable:

# Increase limit to 30,000 characters
export SLASH_COMMAND_TOOL_CHAR_BUDGET=30000

# Then launch Claude Code
claude

This gives you approximately 2x more skill visibility in the system prompt.

Note: This is a temporary workaround. The Claude Code team is working on better solutions for skill discovery and loading.

Token Efficiency

MetricManual SetupWith SkillsSavings
Average Tokens12,000-15,0004,000-5,000~65%
Typical Errors2-4 per service0 (prevented)100%
Setup Time2-4 hours15-45 minutes~80%

Across all 170 skills: 400+ documented errors prevented.

Contributing

Prerequisites for Contributors

Install the official plugin development toolkit:

/plugin install plugin-dev@claude-code-marketplace

This provides:

  • /plugin-dev:create-plugin command (8-phase guided workflow)
  • 7 comprehensive skills (hooks, MCP, structure, agents, commands, skills)
  • 2 specialized agents (agent-creator, plugin-validator)

Quick Steps

  1. Create skill directory in plugins/
  2. Add SKILL.md with YAML frontmatter
  3. Run ./scripts/sync-plugins.sh
  4. Submit pull request

See CONTRIBUTING.md and PLUGIN_DEV_BEST_PRACTICES.md for detailed guidelines.

Documentation

DocumentPurpose
START_HERE.mdStart here! Quick navigation guide
PLUGIN_DEV_BEST_PRACTICES.mdRepository-specific best practices (marketplace, budget, quality)
MARKETPLACE.mdFull skill catalog and installation guide
MARKETPLACE_MANAGEMENT.mdTechnical infrastructure (plugin.json, scripts, validation)
CLAUDE.mdProject context and development standards
CONTRIBUTING.mdContribution guidelines

Links

Built with ❤️ by Claude Skills Maintainers

View source on GitHub

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