test(multiple-subtitles): checkpoint native seek diagnostics [PKG-MULTI-SUB-05]

test/browser/source-restoration.js

@@ -0,0 +1,31 @@
+export async function switchAfterNativeRestoration(page, url) {
+  await page.evaluate((url) => {
+    const art = window.art
+    if (url === art.url)
+      return art.switchUrl(url)
+    const video = art.video
+    let resolveRestored
+    const restored = new Promise((resolve) => {
+      resolveRestored = resolve
+    })
+    const onSeeked = () => resolveRestored()
+    const onMetadata = () => {
+      if (video.seeking)
+        video.addEventListener('seeked', onSeeked, { once: true })
+      else
+        resolveRestored()
+    }
+    const cleanup = () => {
+      video.removeEventListener('loadedmetadata', onMetadata)
+      video.removeEventListener('seeked', onSeeked)
+    }
+    video.addEventListener('loadedmetadata', onMetadata, { once: true })
+    try {
+      return Promise.all([art.switchUrl(url), restored]).then(() => undefined).finally(cleanup)
+    }
+    catch (error) {
+      cleanup()
+      throw error
+    }
+  }, url)
+}