Add separate test for stateful multiplayer client

osu.Game.Tests/OnlinePlay/StatefulMultiplayerClientTest.cs

@@ -0,0 +1,35 @@
+// Copyright (c) ppy Pty Ltd <contact@ppy.sh>. Licensed under the MIT Licence.
+// See the LICENCE file in the repository root for full licence text.
+
+using NUnit.Framework;
+using osu.Framework.Testing;
+using osu.Game.Tests.Visual.Multiplayer;
+using osu.Game.Users;
+
+namespace osu.Game.Tests.OnlinePlay
+{
+    [HeadlessTest]
+    public class StatefulMultiplayerClientTest : MultiplayerTestScene
+    {
+        [Test]
+        public void TestUserAddedOnJoin()
+        {
+            var user = new User { Id = 33 };
+
+            AddRepeatStep("add user multiple times", () => Client.AddUser(user), 3);
+            AddAssert("room has 2 users", () => Client.Room?.Users.Count == 2);
+        }
+
+        [Test]
+        public void TestUserRemovedOnLeave()
+        {
+            var user = new User { Id = 44 };
+
+            AddStep("add user", () => Client.AddUser(user));
+            AddAssert("room has 2 users", () => Client.Room?.Users.Count == 2);
+
+            AddRepeatStep("remove user multiple times", () => Client.RemoveUser(user), 3);
+            AddAssert("room has 1 user", () => Client.Room?.Users.Count == 1);
+        }
+    }
+}