Fix regression with background dim

osu.Game.Tests/Visual/TestCaseBackgroundScreenBeatmap.cs

@@ -0,0 +1,65 @@
+// 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 System;
+using NUnit.Framework.Internal;
+using osu.Framework.Allocation;
+using osu.Game.Configuration;
+using osu.Game.Graphics;
+using osu.Game.Rulesets;
+using osu.Game.Screens;
+using osu.Game.Screens.Backgrounds;
+using osu.Game.Screens.Play;
+
+namespace osu.Game.Tests.Visual
+{
+    public class TestCaseBackgroundScreenBeatmap : TestCasePlayer
+    {
+
+        [BackgroundDependencyLoader]
+        private void load(OsuConfigManager manager)
+        {
+            LoadScreen(new DimAccessiblePlayer());
+        }
+
+        [Test]
+        public void EnableUserDimTest()
+        {
+            AddStep("Test User Dimming", () => ((DimAccessiblePlayer)Player).EnableScreenDim());
+            AddAssert("Check screen dim", () => ((DimAccessiblePlayer)Player).AssertDimState());
+        }
+
+        protected override Player CreatePlayer(Ruleset ruleset) => new DimAccessiblePlayer();
+
+        private class DimAccessiblePlayer : Player
+        {
+            protected override BackgroundScreen CreateBackground() => new FadeAccessibleBackground();
+            public void EnableScreenDim()
+            {
+                Background.UpdateDim.Value = true;
+            }
+
+            public void DisableScreenDim()
+            {
+                Background.UpdateDim.Value = false;
+            }
+
+            public bool AssertDimState()
+            {
+                return ((FadeAccessibleBackground)Background).AssertDimState();
+            }
+
+            private class FadeAccessibleBackground : BackgroundScreenBeatmap
+            {
+                public bool AssertDimState()
+                {
+                    return FadeContainer.Colour == OsuColour.Gray(BackgroundOpacity);
+                }
+            }
+        }
+    }
+
+    internal class SetupAttribute : Attribute
+    {
+    }
+}