testing-patterns

# Testing Patterns

Comprehensive testing patterns including unit tests, integration tests, E2E tests, and mocking strategies for common services.

## When to Use

- Writing new features (TDD)
- Testing API endpoints
- Testing React components
- Mocking external services
- Setting up E2E tests
- Verifying user flows

## Test Types Overview

| Test Type | Scope | Speed | Examples |
|-----------|-------|-------|----------|
| Unit | Individual functions/components | Fast (< 50ms) | Pure functions, utilities, hooks |
| Integration | Multiple components/modules | Medium (< 1s) | API endpoints, database operations |
| E2E | Complete user flows | Slow (2-10s) | Login flow, checkout, search |

## Unit Testing Patterns

### Testing Pure Functions

```typescript
// src/lib/utils.ts
export function calculateProbability(yesVotes: number, noVotes: number): number {
  const total = yesVotes + noVotes
  if (total === 0) return 0.5
  return yesVotes / total
}

// src/lib/utils.test.ts
import { calculateProbability } from './utils'

describe('calculateProbability', () => {
  it('returns 0.5 for equal votes', () => {
    expect(calculateProbability(10, 10)).toBe(0.5)
  })

  it('returns 0.5 for zero votes', () => {
    expect(calculateProbability(0, 0)).toBe(0.5)
  })

  it('calculates correct probability for yes bias', () => {
    expect(calculateProbability(75, 25)).toBe(0.75)
  })

  it('calculates correct probability for no bias', () => {
    expect(calculateProbability(25, 75)).toBe(0.25)
  })

  it('handles edge case of one vote', () => {
    expect(calculateProbability(1, 0)).toBe(1)
    expect(calculateProbability(0, 1)).toBe(0)
  })
})
```

### Testing React Components

```typescript
import { render, screen, fireEvent, waitFor } from '@testing-library/react'
import userEvent from '@testing-library/user-event'
import { MarketCard } from './MarketCard'

describe('MarketCard', () => {
  const mockMarket = {
    id: '1',
    name: 'Test Market',
    description: 'Test descriptio