Preserve player definition order in MapPlayers

OpenRA.Test/OpenRA.Game/MapPlayersTest.cs

@@ -0,0 +1,37 @@
+#region Copyright & License Information
+/*
+ * Copyright (c) The OpenRA Developers and Contributors
+ * This file is part of OpenRA, which is free software. It is made
+ * available to you under the terms of the GNU General Public License
+ * as published by the Free Software Foundation, either version 3 of
+ * the License, or (at your option) any later version. For more
+ * information, see COPYING.
+ */
+#endregion
+
+using NUnit.Framework;
+
+namespace OpenRA.Test
+{
+	[TestFixture]
+	sealed class MapPlayersTest
+	{
+		[TestCase(TestName = "Players keep their definition order when removed and re-added")]
+		public void PlayersKeepDefinitionOrder()
+		{
+			var players = new MapPlayers();
+			string[] names = ["Neutral", "Creeps", "Multi0", "Multi1", "Multi2"];
+			foreach (var name in names)
+				players.Players.Add(name, null);
+
+			// The map editor removes and re-adds all spawn players when updating multiple spawns at once.
+			for (var i = 2; i < names.Length; i++)
+				players.Players.Remove(names[i]);
+
+			for (var i = 2; i < names.Length; i++)
+				players.Players.Add(names[i], null);
+
+			Assert.That(players.Players.Keys, Is.EqualTo(names));
+		}
+	}
+}