test: Add browser tests for the media viewing gallery and viewer (#2661)

tests/browser/fixtures.ts

@@ -0,0 +1,14 @@
+// The media the browser tests use, served by the Vite dev server from where it
+// sits in the tree. Two consumers build URLs to it and a third serves copies of
+// it (`test-media.ts`), so the path and the names are kept in one place.
+const FIXTURES_PATH = '/tests/browser/fixtures';
+
+// A still red image, standing in for anything a camera hands over as a picture:
+// a snapshot, or a live view drawn from stills.
+export const SNAPSHOT_FIXTURE_FILENAME = 'still-red.png';
+
+// Ten seconds of red, standing in for an event's clip. See fixtures/README.md .
+export const CLIP_FIXTURE_FILENAME = 'clip.webm';
+
+export const createFixtureURL = (filename: string): string =>
+  `${FIXTURES_PATH}/${filename}`;