add missing mocking

src/tile/GridTile.test.tsx

@@ -6,7 +6,7 @@ Please see LICENSE in the repository root for full details.
 */
 
 import { type RemoteTrackPublication } from "livekit-client";
-import { test, expect } from "vitest";
+import { test, expect, beforeAll } from "vitest";
 import { render, screen } from "@testing-library/react";
 import { axe } from "vitest-axe";
 import { type MatrixRTCSession } from "matrix-js-sdk/lib/matrixrtc";
@@ -28,6 +28,22 @@ global.IntersectionObserver = class MockIntersectionObserver {
   public disconnect(): void {}
 } as unknown as typeof IntersectionObserver;
 
+// Mock ResizeObserver as it is needed by the useMeasure hook used in the GridTile, but is not implemented in JSDOM.
+// We just need to mock it with empty methods as we don't need to test its functionality here.
+beforeAll(() => {
+  window.ResizeObserver = class ResizeObserver {
+    public observe(): void {
+      // do nothing
+    }
+    public unobserve(): void {
+      // do nothing
+    }
+    public disconnect(): void {
+      // do nothing
+    }
+  };
+});
+
 test("GridTile is accessible", async () => {
   const vm = createRemoteMedia(
     mockRtcMembership("@alice:example.org", "AAAA"),

src/tile/SpotlightTile.test.tsx

@@ -5,7 +5,7 @@ SPDX-License-Identifier: AGPL-3.0-only OR LicenseRef-Element-Commercial
 Please see LICENSE in the repository root for full details.
 */
 
-import { test, expect, vi } from "vitest";
+import { test, expect, vi, beforeAll } from "vitest";
 import { isInaccessible, render, screen } from "@testing-library/react";
 import { axe } from "vitest-axe";
 import userEvent from "@testing-library/user-event";
@@ -27,6 +27,22 @@ global.IntersectionObserver = class MockIntersectionObserver {
   public unobserve(): void {}
 } as unknown as typeof IntersectionObserver;
 
+// Mock ResizeObserver as it is needed by the useMeasure hook used in the SpotlightTile, but is not implemented in JSDOM.
+// We just need to mock it with empty methods as we don't need to test its functionality here.
+beforeAll(() => {
+  window.ResizeObserver = class ResizeObserver {
+    public observe(): void {
+      // do nothing
+    }
+    public unobserve(): void {
+      // do nothing
+    }
+    public disconnect(): void {
+      // do nothing
+    }
+  };
+});
+
 test("SpotlightTile is accessible", async () => {
   const vm1 = createRemoteMedia(
     mockRtcMembership("@alice:example.org", "AAAA"),