Ensure request handling for OnlinePlayTestScene runs in a scheduled fashion

osu.Game/Tests/Visual/OnlinePlay/OnlinePlayTestScene.cs

@@ -2,6 +2,7 @@
 // See the LICENCE file in the repository root for full licence text.
 
 using System;
+using System.Threading.Tasks;
 using NUnit.Framework;
 using osu.Framework.Allocation;
 using osu.Framework.Bindables;
@@ -67,7 +68,24 @@ namespace osu.Game.Tests.Visual.OnlinePlay
             // To get around this, the BeatmapManager is looked up from the dependencies provided to the children of the test scene instead.
             var beatmapManager = dependencies.Get<BeatmapManager>();
 
-            ((DummyAPIAccess)API).HandleRequest = request => handler.HandleRequest(request, API.LocalUser.Value, beatmapManager);
+            ((DummyAPIAccess)API).HandleRequest = request =>
+            {
+                TaskCompletionSource<bool> tcs = new TaskCompletionSource<bool>();
+
+                // Because some of the handlers use realm, we need to ensure the game is still alive when firing.
+                // If we don't, a stray `PerformAsync` could hit an `ObjectDisposedException` if running too late.
+                Scheduler.Add(() =>
+                {
+                    bool result = handler.HandleRequest(request, API.LocalUser.Value, beatmapManager);
+                    tcs.SetResult(result);
+                }, false);
+
+#pragma warning disable RS0030
+                // We can't GetResultSafely() here (will fail with "Can't use GetResultSafely from inside an async operation."), but Wait is safe enough due to
+                // the task being a TaskCompletionSource.
+                return tcs.Task.Result;
+#pragma warning restore RS0030
+            };
         });
 
         /// <summary>