fix: Report media failures once per failure (#2666)

tests/browser/test-media.ts

@@ -75,6 +75,15 @@ export const createUnansweredMediaURL = (): string => createTestMediaURL([]);
 export const createStallingMediaURL = (filename?: string): string =>
   createTestMediaURL([HTTP_OK], false, filename);
 
+/**
+ * How many requests a media URL has been asked for, so a test can count what
+ * the card actually fetched rather than only what it displayed.
+ */
+export const getTestMediaRequestCount = (url: string): number => {
+  const token = new URL(url, window.location.href).searchParams.get('token');
+  return (token ? requestCounts.get(token) : null) ?? 0;
+};
+
 /**
  * Serves a fixture at `/test-media/<file>`, behaving as the query asks:
  *