test: can register service workers in an iframe (#30045)

References #29267.

tests/library/capabilities.spec.ts

@@ -350,3 +350,52 @@ it('service worker should cover the iframe', async ({ page, server }) => {
 
   await expect(page.frameLocator('iframe').locator('div')).toHaveText('from the service worker');
 });
+
+it('service worker should register in an iframe', async ({ page, server }) => {
+  it.info().annotations.push({ type: 'issue', description: 'https://github.com/microsoft/playwright/issues/29267' });
+
+  server.setRoute('/main.html', (req, res) => {
+    res.writeHead(200, { 'content-type': 'text/html' }).end(`
+      <iframe src='/dir/iframe.html'></iframe>
+    `);
+  });
+
+  server.setRoute('/dir/iframe.html', (req, res) => {
+    res.writeHead(200, { 'content-type': 'text/html' }).end(`
+      <script>
+        window.registrationPromise = navigator.serviceWorker.register('sw.js');
+        window.activationPromise = new Promise(resolve => navigator.serviceWorker.oncontrollerchange = resolve);
+      </script>
+    `);
+  });
+
+  server.setRoute('/dir/sw.js', (req, res) => {
+    res.writeHead(200, { 'content-type': 'application/javascript' }).end(`
+      const kIframeHtml = "<div>from the service worker</div>";
+
+      self.addEventListener('fetch', event => {
+        if (event.request.url.endsWith('html')) {
+          event.respondWith(fetch(event.request));
+          return;
+        }
+        const blob = new Blob(['responseFromServiceWorker'], { type: 'text/plain' });
+        const response = new Response(blob, { status: 200 , statusText: 'OK' });
+        event.respondWith(response);
+      });
+
+      self.addEventListener('activate', event => {
+        event.waitUntil(clients.claim());
+      });
+    `);
+  });
+
+  await page.goto(server.PREFIX + '/main.html');
+  const iframe = page.frames()[1];
+  await iframe.evaluate(() => window['activationPromise']);
+
+  const response = await iframe.evaluate(async () => {
+    const response = await fetch('foo.txt');
+    return response.text();
+  });
+  expect(response).toBe('responseFromServiceWorker');
+});