---

name: test-setup description: Setting up tests for new code covering unit tests, integration tests, and test organization

Test Setup Skill

Guidance for writing effective tests, organizing test files, and establishing good testing practices.

When To Use

• Adding tests to new features
• Setting up test infrastructure
• Improving test coverage
• Learning testing patterns

Test Types

Unit Tests

What: Test individual functions/classes in isolation When: Pure logic, utilities, business rules Speed: Fast (milliseconds) Dependencies: Mock external dependencies

Copydescribe('calculateDiscount', () => {
  it('applies 10% discount for premium users', () => {
    const result = calculateDiscount(100, 'premium')
    expect(result).toBe(90)
  })

  it('returns original price for regular users', () => {
    const result = calculateDiscount(100, 'regular')
    expect(result).toBe(100)
  })
})

Integration Tests

What: Test multiple components working together When: API endpoints, database operations, service interactions Speed: Slower (seconds) Dependencies: Use real dependencies or test doubles

Copydescribe('POST /api/users', () => {
  it('creates user and returns 201', async () => {
    const response = await request(app)
      .post('/api/users')
      .send({ name: 'Test User', email: 'test@example.com' })

    expect(response.status).toBe(201)
    expect(response.body.user).toMatchObject({
      name: 'Test User',
      email: 'test@example.com'
    })
  })
})

End-to-End Tests

What: Test complete user workflows When: Critical user paths, full stack verification Speed: Slowest (seconds to minutes)

Test Organization

File Structure

Copyyour-project/
├── src/
│   ├── utils.js
│   └── api/users.js
├── tests/
│   ├── unit/
│   │   └── utils.test.js
│   ├── integration/
│   │   └── api/users.test.js
│   └── e2e/
│       └── checkout.spec.js

Test Structure (AAA Pattern)

Copytest('descriptive test name', () => {
  // Arrange - Set up test data
  const user = { id: 1, name: 'Test' }

  // Act - Execute the code
  const result = service.formatUser(user)

  // Assert - Verify the results
  expect(result).toBe('User: Test')
})

Writing Good Tests

Good Test Names

Copy// Bad
test('it works', ...)
test('test user', ...)

// Good
test('returns 404 when user not found', ...)
test('calculates total including tax', ...)

Test One Thing

Separate tests for each behavior, not one giant test.

Test Edge Cases

Copydescribe('divide', () => {
  it('divides two positive numbers', () => {
    expect(divide(10, 2)).toBe(5)
  })

  it('throws when dividing by zero', () => {
    expect(() => divide(10, 0)).toThrow('Division by zero')
  })
})

Mocking

When to Mock

Mock:

• API calls
• Database queries
• External services
• Time/dates

Don't mock:

• Code you're testing
• Simple utilities
• Your own business logic

Test Coverage

What to Aim For

• Critical paths: 100% coverage
• Business logic: 90%+ coverage
• Utilities: 80%+ coverage
• UI components: Behavior over coverage %

Coverage is not Quality

Good: High coverage with meaningful assertions Bad: High coverage with weak assertions

Checklist

When writing tests:

• Test name describes what's being tested
• Test is focused (tests one thing)
• Edge cases covered
• Assertions are meaningful
• External dependencies mocked
• Tests are independent (no shared state)
• Tests run fast

Remember

• Tests are documentation
• Good tests catch bugs before production
• Fast tests encourage running them often
• Flaky tests erode confidence
• Tests should be as simple as possible