E2etesting

E2E Testing — Playwright / TypeScript

Staff Engineer standard: E2E tests cover critical flows only — they're expensive, so spend them where unit tests can't reach.

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1. When to Reach for Playwright

✅ USE FOR:                          ❌ DON'T USE FOR:
- Critical user flows                 - Logic unit tests (use Vitest)
  (login, signup, checkout, payment)  - Component-level tests (use RTL)
- Cross-browser regressions           - Pure functions (use Vitest)
- Auth + session persistence          - Anything you can mock cheaply
- Visual regression (snapshots)

Rule of thumb: if breakage would page someone at 2am, it deserves an E2E test.

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2. Installation & Structure

pnpm create playwright@latest

tests/e2e/
├── playwright.config.ts     # Config (browsers, base URL, retries)
├── fixtures/                # Test data, auth helpers
├── pages/                   # Page Object Models
│   ├── login.page.ts
│   └── dashboard.page.ts
└── specs/                   # Test files
    ├── auth.spec.ts
    └── checkout.spec.ts

POMs separate what the page is from what the test does. Without POMs, refactoring a form selector means editing every spec.

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3. Configuration

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

export default defineConfig({
  testDir: "./tests/e2e/specs",
  timeout: 30_000,
  retries: process.env.CI ? 2 : 0,   // retry only in CI — local flakes need fixing
  workers: process.env.CI ? 1 : undefined,
  reporter: [["html"], ["list"]],

  use: {
    baseURL: process.env.BASE_URL ?? "http://localhost:3000",
    screenshot: "only-on-failure",
    video: "retain-on-failure",
    trace: "on-first-retry",
  },

  projects: [
    { name: "chromium", use: { ...devices["Desktop Chrome"] } },
    { name: "firefox",  use: { ...devices["Desktop Firefox"] } },
    { name: "webkit",   use: { ...devices["Desktop Safari"] } },
  ],
});

Why these defaults:

• retries: 2 in CI hides infra flakes (network, cold start); locally 0 forces you to fix the spec
• trace: "on-first-retry" — full timeline + DOM snapshots, only when needed (large files)
• workers: 1 in CI avoids race conditions on shared backend state

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4. Page Object Model

// pages/login.page.ts
import { Page, Locator, expect } from "@playwright/test";

export class LoginPage {
  readonly emailInput: Locator;
  readonly passwordInput: Locator;
  readonly submitButton: Locator;
  readonly errorMessage: Locator;

  constructor(private readonly page: Page) {
    this.emailInput    = page.getByTestId("email-input");
    this.passwordInput = page.getByTestId("password-input");
    this.submitButton  = page.getByRole("button", { name: /sign in/i });
    this.errorMessage  = page.getByTestId("error-message");
  }

  async goto() {
    await this.page.goto("/login");
  }

  async login(email: string, password: string) {
    await this.emailInput.fill(email);
    await this.passwordInput.fill(password);
    await this.submitButton.click();
  }

  async expectError(message: string | RegExp) {
    await expect(this.errorMessage).toContainText(message);
  }
}

Rules:

• One POM per page or major section
• Locators live in the constructor — refactor-friendly
• Methods describe user intent (login()), not mechanics (clickAndType())

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5. Writing Specs

// specs/auth.spec.ts
import { test, expect } from "@playwright/test";
import { LoginPage } from "../pages/login.page";

test.describe("Authentication", () => {
  test("successful login redirects to dashboard", async ({ page }) => {
    const login = new LoginPage(page);
    await login.goto();
    await login.login("[email protected]", "validPassword123");

    await expect(page).toHaveURL("/dashboard");
    await expect(page.getByRole("heading", { name: /welcome/i })).toBeVisible();
  });

  test("invalid credentials show error", async ({ page }) => {
    const login = new LoginPage(page);
    await login.goto();
    await login.login("[email protected]", "wrongPassword");

    await login.expectError(/invalid credentials/i);
  });
});

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6. Selector Priority

// ✅ BEST — stable, intentional
page.getByTestId("submit-button");

// ✅ GOOD — accessibility-friendly, survives copy changes via name regex
page.getByRole("button", { name: /submit/i });

// ⚠️ OK — for unique static text
page.getByText("Submit order");

// ❌ AVOID — couples test to styling
page.locator(".btn-primary-xl");

// ❌ AVOID — couples test to DOM structure
page.locator("form > div:nth-child(3) > button");

Pattern: add data-testid to interactive elements as you build them — retrofitting tests later is twice the work.

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7. Auth Reuse — Avoid Logging In Every Test

// playwright.config.ts
projects: [
  {
    name: "setup",
    testMatch: /global\.setup\.ts/,
  },
  {
    name: "chromium",
    use: { ...devices["Desktop Chrome"], storageState: "playwright/.auth/user.json" },
    dependencies: ["setup"],
  },
],

// global.setup.ts — runs once, persists session
import { test as setup } from "@playwright/test";

setup("authenticate", async ({ page }) => {
  await page.goto("/login");
  await page.getByTestId("email-input").fill(process.env.TEST_EMAIL!);
  await page.getByTestId("password-input").fill(process.env.TEST_PASSWORD!);
  await page.getByRole("button", { name: /sign in/i }).click();
  await page.waitForURL("/dashboard");
  await page.context().storageState({ path: "playwright/.auth/user.json" });
});

Cuts spec time by ~80% on auth-heavy suites.

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8. Running Tests

pnpm exec playwright test                  # All specs, all browsers
pnpm exec playwright test auth.spec.ts     # Single file
pnpm exec playwright test --headed         # Watch the browser
pnpm exec playwright test --debug          # Inspector + step-through
pnpm exec playwright test --ui             # Time-travel UI (best DX)
pnpm exec playwright show-report           # HTML report after run

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9. CI Integration

# .github/workflows/e2e.yml
name: E2E Tests
on: [push, pull_request]

jobs:
  e2e:
    runs-on: ubuntu-latest
    steps:
      - uses: actions/checkout@v4
      - uses: pnpm/action-setup@v4
        with: { version: 9 }
      - uses: actions/setup-node@v4
        with:
          node-version: 20
          cache: "pnpm"
      - run: pnpm install --frozen-lockfile
      - run: pnpm exec playwright install --with-deps
      - run: pnpm exec playwright test
      - uses: actions/upload-artifact@v4
        if: failure()
        with:
          name: playwright-report
          path: playwright-report/
          retention-days: 7

Artifacts on failure only — passing runs don't need 50MB of video evidence.

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10. Flaky Test Triage

1. Reproduce locally with --repeat-each=10
2. Open trace: pnpm exec playwright show-trace trace.zip
3. Common culprits:
   - waitForSelector instead of web-first assertions (expect().toBeVisible())
   - Network races — use page.waitForResponse() or route().fulfill()
   - Animation timing — disable via CSS or wait for stable state
   - Shared backend state — isolate via test-scoped users/data

Rule: a flake fixed by retry is a bug deferred, not solved.

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11. Deep-Dive References

references/ holds the full Playwright best-practices library:

Subdir	Contents
core/	Locators, assertions, fixtures, page objects
browser-apis/	Network interception, file uploads, dialogs, geolocation
testing-patterns/	Auth, data isolation, visual testing, API mocking
debugging/	Trace viewer, inspector, video, slow-mo
architecture/	Multi-project setup, custom workers, shared state
frameworks/	React/Vue/Angular-specific patterns
infrastructure-ci-cd/	Docker, GitHub Actions, sharding, parallelism
advanced/	Custom reporters, component testing, Playwright API

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12. Quick Checklist

[ ] data-testid on every interactive element
[ ] POM per page — no raw locators in specs
[ ] storageState reused for auth-required tests
[ ] Web-first assertions (expect().toBeVisible()) — not waitFor*
[ ] Specs cover critical flows only (login/checkout/payment)
[ ] CI runs against ephemeral test users, not prod data
[ ] Failure artifacts uploaded (screenshots, video, trace)
[ ] No skipped/disabled specs without an open ticket link