tdd-workflow

name	tdd-workflow
description	Use this skill when writing new features, fixing bugs, or refactoring code. Enforces test-driven development with 80%+ coverage including unit, integration, and E2E tests.

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:

describe('Semantic Search', () => {
  it('returns relevant markets for query', async () => {
    // Test implementation
  })

  it('handles empty query gracefully', async () => {
    // Test edge case
  })

  it('falls back to substring search when service unavailable', async () => {
    // Test fallback behavior
  })

  it('sorts results by similarity score', async () => {
    // Test sorting logic
  })
})

Step 3: Run Tests (They Should Fail)

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

Step 4: Implement Code

Write minimal code to make tests pass.

Step 5: Run Tests Again

npm test
# 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

npm run test:coverage
# Verify 80%+ coverage achieved

Testing Patterns

Unit Test Pattern (Jest/Vitest)

import { render, screen, fireEvent } from '@testing-library/react'
import { Button } from './Button'

describe('Button Component', () => {
  it('renders with correct text', () => {
    render(<Button>Click me</Button>)
    expect(screen.getByText('Click me')).toBeInTheDocument()
  })

  it('calls onClick when clicked', () => {
    const handleClick = jest.fn()
    render(<Button onClick={handleClick}>Click</Button>)

    fireEvent.click(screen.getByRole('button'))

    expect(handleClick).toHaveBeenCalledTimes(1)
  })
})

API Integration Test Pattern

import { NextRequest } from 'next/server'
import { GET } from './route'

describe('GET /api/markets', () => {
  it('returns markets successfully', async () => {
    const request = new NextRequest('http://localhost/api/markets')
    const response = await GET(request)
    const data = await response.json()

    expect(response.status).toBe(200)
    expect(data.success).toBe(true)
    expect(Array.isArray(data.data)).toBe(true)
  })

  it('validates query parameters', async () => {
    const request = new NextRequest('http://localhost/api/markets?limit=invalid')
    const response = await GET(request)

    expect(response.status).toBe(400)
  })
})

E2E Test Pattern (Playwright)

import { test, expect } from '@playwright/test'

test('user can search and filter markets', async ({ page }) => {
  await page.goto('/')
  await page.click('a[href="/markets"]')

  await expect(page.locator('h1')).toContainText('Markets')

  await page.fill('input[placeholder="Search markets"]', 'election')
  await page.waitForTimeout(600)

  const results = page.locator('[data-testid="market-card"]')
  await expect(results).toHaveCount(5, { timeout: 5000 })
})

Coverage Thresholds

{
  "coverageThreshold": {
    "global": {
      "branches": 80,
      "functions": 80,
      "lines": 80,
      "statements": 80
    }
  }
}

Common Testing Mistakes to Avoid

Testing Implementation Details

// Don't test internal state
expect(component.state.count).toBe(5)  // BAD

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

Brittle Selectors

// Breaks easily
await page.click('.css-class-xyz')  // BAD

// Resilient to changes
await page.click('[data-testid="submit-button"]')  // GOOD

No Test Isolation

// Tests depend on each other - BAD
test('creates user', () => { /* ... */ })
test('updates same user', () => { /* depends on previous test */ })

// Each test sets up its own data - GOOD
test('updates user', () => {
  const user = createTestUser()
  // Update logic
})

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

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