Test-Driven Development Workflow

This skill ensures all code development follows TDD principles with comprehensive test coverage.

When to Activate

• Writing new features or functionality
• Fixing bugs or issues
• Refactoring existing code
• Adding API endpoints
• Creating new components

Core Principles

1. Tests BEFORE Code

ALWAYS write tests first, then implement code to make tests pass.

2. Coverage Requirements

• Minimum 80% coverage (unit + integration + E2E)
• All edge cases covered
• Error scenarios tested
• Boundary conditions verified

3. Test Types

Unit Tests

• Individual functions and utilities
• Component logic
• Pure functions
• Helpers and utilities

Integration Tests

• API endpoints
• Database operations
• Service interactions
• External API calls

E2E Tests (Playwright)

• Critical user flows
• Complete workflows
• Browser automation
• UI interactions

TDD Workflow Steps

Step 1: Write User Journeys

As a [role], I want to [action], so that [benefit]

Example:
As a user, I want to search for markets semantically,
so that I can find relevant markets even without exact keywords.

Step 2: Generate Test Cases

For each user journey, create comprehensive test cases:

typescript
1describe('Semantic Search', () => {
2  it('returns relevant markets for query', async () => {
3    // Test implementation
4  })
5
6  it('handles empty query gracefully', async () => {
7    // Test edge case
8  })
9
10  it('falls back to substring search when Redis unavailable', async () => {
11    // Test fallback behavior
12  })
13
14  it('sorts results by similarity score', async () => {
15    // Test sorting logic
16  })
17})

Step 3: Run Tests (They Should Fail)

bash
1npm test
2# Tests should fail - we haven't implemented yet

Step 4: Implement Code

Write minimal code to make tests pass:

typescript
1// Implementation guided by tests
2export async function searchMarkets(query: string) {
3  // Implementation here
4}

Step 5: Run Tests Again

bash
1npm test
2# Tests should now pass

Step 6: Refactor

Improve code quality while keeping tests green:

• Remove duplication
• Improve naming
• Optimize performance
• Enhance readability

Step 7: Verify Coverage

bash
1npm run test:coverage
2# Verify 80%+ coverage achieved

Testing Patterns

Unit Test Pattern (Jest/Vitest)

typescript
1import { render, screen, fireEvent } from '@testing-library/react'
2import { Button } from './Button'
3
4describe('Button Component', () => {
5  it('renders with correct text', () => {
6    render(<Button>Click me</Button>)
7    expect(screen.getByText('Click me')).toBeInTheDocument()
8  })
9
10  it('calls onClick when clicked', () => {
11    const handleClick = jest.fn()
12    render(<Button onClick={handleClick}>Click</Button>)
13
14    fireEvent.click(screen.getByRole('button'))
15
16    expect(handleClick).toHaveBeenCalledTimes(1)
17  })
18
19  it('is disabled when disabled prop is true', () => {
20    render(<Button disabled>Click</Button>)
21    expect(screen.getByRole('button')).toBeDisabled()
22  })
23})

API Integration Test Pattern

typescript
1import { NextRequest } from 'next/server'
2import { GET } from './route'
3
4describe('GET /api/markets', () => {
5  it('returns markets successfully', async () => {
6    const request = new NextRequest('http://localhost/api/markets')
7    const response = await GET(request)
8    const data = await response.json()
9
10    expect(response.status).toBe(200)
11    expect(data.success).toBe(true)
12    expect(Array.isArray(data.data)).toBe(true)
13  })
14
15  it('validates query parameters', async () => {
16    const request = new NextRequest('http://localhost/api/markets?limit=invalid')
17    const response = await GET(request)
18
19    expect(response.status).toBe(400)
20  })
21
22  it('handles database errors gracefully', async () => {
23    // Mock database failure
24    const request = new NextRequest('http://localhost/api/markets')
25    // Test error handling
26  })
27})

E2E Test Pattern (Playwright)

typescript
1import { test, expect } from '@playwright/test'
2
3test('user can search and filter markets', async ({ page }) => {
4  // Navigate to markets page
5  await page.goto('/')
6  await page.click('a[href="/markets"]')
7
8  // Verify page loaded
9  await expect(page.locator('h1')).toContainText('Markets')
10
11  // Search for markets
12  await page.fill('input[placeholder="Search markets"]', 'election')
13
14  // Wait for debounce and results
15  await page.waitForTimeout(600)
16
17  // Verify search results displayed
18  const results = page.locator('[data-testid="market-card"]')
19  await expect(results).toHaveCount(5, { timeout: 5000 })
20
21  // Verify results contain search term
22  const firstResult = results.first()
23  await expect(firstResult).toContainText('election', { ignoreCase: true })
24
25  // Filter by status
26  await page.click('button:has-text("Active")')
27
28  // Verify filtered results
29  await expect(results).toHaveCount(3)
30})
31
32test('user can create a new market', async ({ page }) => {
33  // Login first
34  await page.goto('/creator-dashboard')
35
36  // Fill market creation form
37  await page.fill('input[name="name"]', 'Test Market')
38  await page.fill('textarea[name="description"]', 'Test description')
39  await page.fill('input[name="endDate"]', '2025-12-31')
40
41  // Submit form
42  await page.click('button[type="submit"]')
43
44  // Verify success message
45  await expect(page.locator('text=Market created successfully')).toBeVisible()
46
47  // Verify redirect to market page
48  await expect(page).toHaveURL(/\/markets\/test-market/)
49})

Test File Organization

src/
├── components/
│   ├── Button/
│   │   ├── Button.tsx
│   │   ├── Button.test.tsx          # Unit tests
│   │   └── Button.stories.tsx       # Storybook
│   └── MarketCard/
│       ├── MarketCard.tsx
│       └── MarketCard.test.tsx
├── app/
│   └── api/
│       └── markets/
│           ├── route.ts
│           └── route.test.ts         # Integration tests
└── e2e/
    ├── markets.spec.ts               # E2E tests
    ├── trading.spec.ts
    └── auth.spec.ts

Mocking External Services

Supabase Mock

typescript
1jest.mock('@/lib/supabase', () => ({
2  supabase: {
3    from: jest.fn(() => ({
4      select: jest.fn(() => ({
5        eq: jest.fn(() => Promise.resolve({
6          data: [{ id: 1, name: 'Test Market' }],
7          error: null
8        }))
9      }))
10    }))
11  }
12}))

Redis Mock

typescript
1jest.mock('@/lib/redis', () => ({
2  searchMarketsByVector: jest.fn(() => Promise.resolve([
3    { slug: 'test-market', similarity_score: 0.95 }
4  ])),
5  checkRedisHealth: jest.fn(() => Promise.resolve({ connected: true }))
6}))

OpenAI Mock

typescript
1jest.mock('@/lib/openai', () => ({
2  generateEmbedding: jest.fn(() => Promise.resolve(
3    new Array(1536).fill(0.1) // Mock 1536-dim embedding
4  ))
5}))

Test Coverage Verification

Run Coverage Report

bash
1npm run test:coverage

Coverage Thresholds

json
1{
2  "jest": {
3    "coverageThresholds": {
4      "global": {
5        "branches": 80,
6        "functions": 80,
7        "lines": 80,
8        "statements": 80
9      }
10    }
11  }
12}

Common Testing Mistakes to Avoid

❌ WRONG: Testing Implementation Details

typescript
1// Don't test internal state
2expect(component.state.count).toBe(5)

✅ CORRECT: Test User-Visible Behavior

typescript
1// Test what users see
2expect(screen.getByText('Count: 5')).toBeInTheDocument()

❌ WRONG: Brittle Selectors

typescript
1// Breaks easily
2await page.click('.css-class-xyz')

✅ CORRECT: Semantic Selectors

typescript
1// Resilient to changes
2await page.click('button:has-text("Submit")')
3await page.click('[data-testid="submit-button"]')

❌ WRONG: No Test Isolation

typescript
1// Tests depend on each other
2test('creates user', () => { /* ... */ })
3test('updates same user', () => { /* depends on previous test */ })

✅ CORRECT: Independent Tests

typescript
1// Each test sets up its own data
2test('creates user', () => {
3  const user = createTestUser()
4  // Test logic
5})
6
7test('updates user', () => {
8  const user = createTestUser()
9  // Update logic
10})

Continuous Testing

Watch Mode During Development

bash
1npm test -- --watch
2# Tests run automatically on file changes

Pre-Commit Hook

bash
1# Runs before every commit
2npm test && npm run lint

CI/CD Integration

yaml
1# GitHub Actions
2- name: Run Tests
3  run: npm test -- --coverage
4- name: Upload Coverage
5  uses: codecov/codecov-action@v3

Best Practices

1. Write Tests First - Always TDD
2. One Assert Per Test - Focus on single behavior
3. Descriptive Test Names - Explain what's tested
4. Arrange-Act-Assert - Clear test structure
5. Mock External Dependencies - Isolate unit tests
6. Test Edge Cases - Null, undefined, empty, large
7. Test Error Paths - Not just happy paths
8. Keep Tests Fast - Unit tests < 50ms each
9. Clean Up After Tests - No side effects
10. Review Coverage Reports - Identify gaps

Success Metrics

• 80%+ code coverage achieved
• All tests passing (green)
• No skipped or disabled tests
• Fast test execution (< 30s for unit tests)
• E2E tests cover critical user flows
• Tests catch bugs before production

Remember: Tests are not optional. They are the safety net that enables confident refactoring, rapid development, and production reliability.