Update spec/dummy/README.md with Playwright testing documentation

- Add comprehensive Playwright testing section to dummy app README
- Include setup instructions for Playwright
- Document all available test commands
- Explain test structure and file organization
- Provide example for writing new Playwright tests
- Link to detailed Playwright README for more information

This ensures developers working with the dummy app understand
how to use Playwright for E2E testing alongside RSpec and Jest.

🤖 Generated with [Claude Code](https://claude.ai/code)

Co-Authored-By: Claude <[email protected]>

Author: justin808

spec/dummy/README.md

@@ -46,3 +46,86 @@ foreman start -f Procfile.dev-static-assets
 ```sh
 foreman start -f Procfile.spec
 ```
+
+# Testing
+
+## Running RSpec Tests
+
+```sh
+bundle exec rspec
+```
+
+## Running Jest Tests
+
+```sh
+yarn test:js
+```
+
+## Running Playwright E2E Tests
+
+Playwright provides cross-browser end-to-end testing for React on Rails components.
+
+### Setup Playwright
+
+```sh
+# Install Playwright and browsers (first time only)
+yarn add -D @playwright/test
+yarn playwright install --with-deps
+```
+
+### Run Playwright Tests
+
+```sh
+# Run all tests in headless mode
+yarn test:e2e
+
+# Run tests with UI (interactive debugging)
+yarn test:e2e:ui
+
+# Run tests with visible browser
+yarn test:e2e:headed
+
+# Debug a specific test
+yarn test:e2e:debug
+
+# View test report
+yarn test:e2e:report
+
+# Run tests in a specific browser
+yarn playwright test --project=chromium
+yarn playwright test --project=firefox
+yarn playwright test --project=webkit
+```
+
+### Playwright Test Structure
+
+Tests are located in `playwright/tests/`:
+
+- `basic-react-components.spec.ts` - Component rendering and interactions
+- `turbolinks-integration.spec.ts` - Turbolinks/Turbo integration
+- `error-handling.spec.ts` - Error monitoring and handling
+- `performance.spec.ts` - Performance and memory testing
+
+Configuration is in `playwright.config.ts`. Test helpers are in `playwright/fixtures/`.
+
+### Writing New Playwright Tests
+
+Create new test files in `playwright/tests/`:
+
+```typescript
+import { test, expect } from '@playwright/test';
+
+test('my new test', async ({ page }) => {
+  await page.goto('/');
+
+  // Test React on Rails component
+  const component = page.locator('#MyComponent-react-component-0');
+  await expect(component).toBeVisible();
+
+  // Interact with component
+  await component.locator('button').click();
+  await expect(component.locator('.result')).toHaveText('Success');
+});
+```
+
+For more details, see the [Playwright README](playwright/README.md).