Add TestCase for main menu ButtonSystem.

osu.Desktop.VisualTests/Tests/TestCaseMenuButtonSystem.cs

@@ -0,0 +1,21 @@
+//Copyright (c) 2007-2016 ppy Pty Ltd <contact@ppy.sh>.
+//Licensed under the MIT Licence - https://raw.githubusercontent.com/ppy/osu/master/LICENCE
+
+using osu.Framework.GameModes.Testing;
+using osu.Game.GameModes.Menu;
+
+namespace osu.Desktop.Tests
+{
+    class TestCaseMenuButtonSystem : TestCase
+    {
+        public override string Name => @"ButtonSystem";
+        public override string Description => @"Main menu button system";
+
+        public override void Reset()
+        {
+            base.Reset();
+
+            Add(new ButtonSystem());
+        }
+    }
+}