e2e-testing-patterns

# E2E Testing Patterns

Build reliable, fast, and maintainable end-to-end test suites that provide confidence to ship code quickly and catch regressions before users do.

## When to Use This Skill

- Implementing end-to-end test automation
- Debugging flaky or unreliable tests
- Testing critical user workflows
- Setting up CI/CD test pipelines
- Testing across multiple browsers
- Validating accessibility requirements
- Testing responsive designs
- Establishing E2E testing standards

## Core Concepts

### 1. E2E Testing Fundamentals

**What to Test with E2E:**

- Critical user journeys (login, checkout, signup)
- Complex interactions (drag-and-drop, multi-step forms)
- Cross-browser compatibility
- Real API integration
- Authentication flows

**What NOT to Test with E2E:**

- Unit-level logic (use unit tests)
- API contracts (use integration tests)
- Edge cases (too slow)
- Internal implementation details

### 2. Test Philosophy

**The Testing Pyramid:**

```
        /\
       /E2E\         ← Few, focused on critical paths
      /─────\
     /Integr\        ← More, test component interactions
    /────────\
   /Unit Tests\      ← Many, fast, isolated
  /────────────\
```

**Best Practices:**

- Test user behavior, not implementation
- Keep tests independent
- Make tests deterministic
- Optimize for speed
- Use data-testid, not CSS selectors

## Playwright Patterns

### Setup and Configuration

```typescript
// playwright.config.ts
import { defineConfig, devices } from "@playwright/test";

export default defineConfig({
  testDir: "./e2e",
  timeout: 30000,
  expect: {
    timeout: 5000,
  },
  fullyParallel: true,
  forbidOnly: !!process.env.CI,
  retries: process.env.CI ? 2 : 0,
  workers: process.env.CI ? 1 : undefined,
  reporter: [["html"], ["junit", { outputFile: "results.xml" }]],
  use: {
    baseURL: "http://localhost:3000",
    trace: "on-first-retry",
    screenshot: "only-on-failure",
    video: "retain-on-failure",
  },
  projects: [
    { name: "chromium"