Add test coverage of `SpectatorPlayer` failing to seek on inopportune frame arrival time

osu.Game.Tests/Visual/Gameplay/TestSceneSpectator.cs

@@ -70,6 +70,56 @@ public void SetupSteps()
             });
         }
 
+        [Test]
+        public void TestSeekToGameplayStartFramesArriveAfterPlayerLoad()
+        {
+            const double gameplay_start = 10000;
+
+            loadSpectatingScreen();
+
+            start();
+
+            waitForPlayer();
+
+            sendFrames(startTime: gameplay_start);
+
+            AddAssert("time is greater than seek target", () => currentFrameStableTime > gameplay_start);
+        }
+
+        /// <summary>
+        /// Tests the same as <see cref="TestSeekToGameplayStartFramesArriveAfterPlayerLoad"/> but with the frames arriving just as <see cref="Player"/> is transitioning into existence.
+        /// </summary>
+        [Test]
+        public void TestSeekToGameplayStartFramesArriveAsPlayerLoaded()
+        {
+            const double gameplay_start = 10000;
+
+            loadSpectatingScreen();
+
+            start();
+
+            AddUntilStep("wait for player loader", () => (Stack.CurrentScreen as PlayerLoader)?.IsLoaded == true);
+
+            AddUntilStep("queue send frames on player load", () =>
+            {
+                var loadingPlayer = (Stack.CurrentScreen as PlayerLoader)?.CurrentPlayer;
+
+                if (loadingPlayer == null)
+                    return false;
+
+                loadingPlayer.OnLoadComplete += _ =>
+                {
+                    spectatorClient.SendFramesFromUser(streamingUser.Id, 10, gameplay_start);
+                };
+                return true;
+            });
+
+            waitForPlayer();
+
+            AddUntilStep("state is playing", () => spectatorClient.WatchedUserStates[streamingUser.Id].State == SpectatedUserState.Playing);
+            AddAssert("time is greater than seek target", () => currentFrameStableTime > gameplay_start);
+        }
+
         [Test]
         public void TestFrameStarvationAndResume()
         {
@@ -319,9 +369,9 @@ private double currentFrameStableTime
         private void checkPaused(bool state) =>
             AddUntilStep($"game is {(state ? "paused" : "playing")}", () => player.ChildrenOfType<DrawableRuleset>().First().IsPaused.Value == state);
 
-        private void sendFrames(int count = 10)
+        private void sendFrames(int count = 10, double startTime = 0)
         {
-            AddStep("send frames", () => spectatorClient.SendFramesFromUser(streamingUser.Id, count));
+            AddStep("send frames", () => spectatorClient.SendFramesFromUser(streamingUser.Id, count, startTime));
         }
 
         private void loadSpectatingScreen()

osu.Game/Tests/Visual/Spectator/TestSpectatorClient.cs

@@ -88,7 +88,8 @@ public void SendEndPlay(int userId, SpectatedUserState state = SpectatedUserStat
         /// </summary>
         /// <param name="userId">The user to send frames for.</param>
         /// <param name="count">The total number of frames to send.</param>
-        public void SendFramesFromUser(int userId, int count)
+        /// <param name="startTime">The time to start gameplay frames from.</param>
+        public void SendFramesFromUser(int userId, int count, double startTime = 0)
         {
             var frames = new List<LegacyReplayFrame>();
 
@@ -102,7 +103,7 @@ public void SendFramesFromUser(int userId, int count)
                     flush();
 
                 var buttonState = currentFrameIndex == lastFrameIndex ? ReplayButtonState.None : ReplayButtonState.Left1;
-                frames.Add(new LegacyReplayFrame(currentFrameIndex * 100, RNG.Next(0, 512), RNG.Next(0, 512), buttonState));
+                frames.Add(new LegacyReplayFrame(currentFrameIndex * 100 + startTime, RNG.Next(0, 512), RNG.Next(0, 512), buttonState));
             }
 
             flush();