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.
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Install
Works with every agent the skills CLI supports.
npx skills add https://github.com/secondsky/claude-skills --skill test-quality-analysis- 01
Install
Run the command in your project. The CLI asks which agents to install for.
- 02
Describe the task
Ask your agent for something this skill covers. It loads test-quality-analysis automatically when relevant.
- 03
Review the result
The agent follows the SKILL.md steps, scripts and references bundled with the skill.
SKILL.md
The instructions your agent reads when the skill is triggered.
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.
// ❌ 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.
// ❌ 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.
// ❌ 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
// ❌ 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
# 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)
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
// ❌ 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
// ❌ 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 testingplaywright-testing- E2E testingmutation-testing- Validate test effectiveness
FAQ
What does the test-quality-analysis skill do?
Detect test smells, overmocking, flaky tests, and coverage issues. Analyze test effectiveness, maintainability, and reliability. Use when reviewing tests or improving test quality.
How do I install test-quality-analysis?
Run npx skills add https://github.com/secondsky/claude-skills --skill test-quality-analysis in your project. The skills CLI detects the agents you use and copies the skill into the right folder. For Claude Code you can also place the skill folder at ~/.claude/skills/test-quality-analysis/ (personal) or .claude/skills/test-quality-analysis/ (project).
Which AI agents can use test-quality-analysis?
Any agent that supports the open Agent Skills format (a folder with a SKILL.md file), including Claude Code, Codex, Cursor, GitHub Copilot, Gemini CLI, Windsurf, Cline, OpenCode and more.
Is test-quality-analysis safe to install?
No partner security audit is available yet. Skills can run commands and scripts, so read the SKILL.md and any bundled files before installing.
Who maintains test-quality-analysis?
It is published by secondsky in secondsky/claude-skills. It has 453 recorded installs.
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