Add e2e test for preview existing post

tests/e2e/specs/posts/preview-existing-post.test.js

@@ -0,0 +1,66 @@
+/**
+ * WordPress dependencies
+ */
+const { test, expect } = require('@wordpress/e2e-test-utils-playwright');
+
+test.describe('Preview Existing Post', () => {
+  test.beforeEach(async ({ admin, editor }, testInfo) => {
+    const title = 'preview post';
+    testInfo.data = { title };
+    await admin.createNewPost({ title });
+    await editor.publishPost();
+  });
+
+  test.afterEach(async ({ requestUtils }, testInfo) => {
+    const { title } = testInfo.data;
+    await requestUtils.deleteAllPosts();
+  });
+
+/**
+ * Selects a menu item radio by its name and verifies `aria-checked=true`.
+ *
+ * @param {Page} page - The Playwright page instance.
+ * @param {string} menuItem - The name of the menu item to select (e.g., 'Tablet', 'Mobile', 'Desktop').
+ */
+  async function selectMenuItemRadio(page, menuItem) {
+    const menuItemRadio = page.getByRole('menuitemradio', { name: menuItem });
+
+    // Click the menu item radio
+    await menuItemRadio.click();
+
+    // Assert that `aria-checked=true` after the click
+    await expect(menuItemRadio).toHaveAttribute('aria-checked', 'true');
+  }
+
+  test('Can Preview Existing Post', async ({ page, admin }, testInfo) => {
+    const { title } = testInfo.data;
+
+    // Navigate to Posts list
+    await admin.visitAdminPage('/');
+    await page.getByRole('link', { name: 'Posts', exact: true }).click();
+
+    //Click on the Test Post.
+    await page.locator(`text="${title}"`).first().click();
+
+    // Click Preview button 
+    await page.getByRole('button', { name: 'View', exact: true }).click();
+
+    // Test for 'Tablet'
+    await selectMenuItemRadio(page, 'Tablet');
+
+    // Test for 'Mobile'
+    await selectMenuItemRadio(page, 'Mobile');
+
+    // Test for 'Desktop'
+    await selectMenuItemRadio(page, 'Desktop');
+
+    // Open Preview in a new tab
+    const [popup] = await Promise.all([
+      page.waitForEvent('popup'),
+      page.locator('text="Preview in new tab"').click(),
+    ]);
+    await popup.waitForLoadState();
+    await expect(popup).toHaveURL(/preview=true/);
+    await expect(popup.locator('body')).toContainText(title);
+  });
+});