Detect test smells, overmocking, flaky tests, and coverage issues. Analyze test effectiveness, maintainability, and reliability. Use when reviewing tests or improving test quality.
/plugin marketplace add secondsky/claude-skills/plugin install test-quality-analysis@claude-skillsThis skill is limited to using the following tools:
Expert knowledge for analyzing and improving test quality - detecting test smells, overmocking, insufficient coverage, and testing anti-patterns.
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).
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()
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()
})
// ❌ 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',
})
})
# 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
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')
})
// ❌ 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
// ❌ 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()
vitest-testing - TypeScript/JavaScript testingplaywright-testing - E2E testingmutation-testing - Validate test effectiveness