Add failing test coverage of legacy fallback lookups

osu.Game.Tests/Skins/TestSceneSkinProvidingContainer.cs

@@ -3,28 +3,61 @@
 
 #nullable disable
 
+using System;
 using System.Collections.Generic;
 using System.Linq;
+using JetBrains.Annotations;
 using NUnit.Framework;
 using osu.Framework.Allocation;
+using osu.Framework.Audio;
 using osu.Framework.Audio.Sample;
 using osu.Framework.Bindables;
 using osu.Framework.Graphics;
 using osu.Framework.Graphics.Rendering;
 using osu.Framework.Graphics.Textures;
+using osu.Framework.IO.Stores;
+using osu.Framework.Platform;
 using osu.Framework.Testing;
 using osu.Game.Audio;
+using osu.Game.Database;
+using osu.Game.IO;
 using osu.Game.Skinning;
 using osu.Game.Tests.Visual;
 
 namespace osu.Game.Tests.Skins
 {
     [HeadlessTest]
-    public partial class TestSceneSkinProvidingContainer : OsuTestScene
+    public partial class TestSceneSkinProvidingContainer : OsuTestScene, IStorageResourceProvider
     {
         [Resolved]
         private IRenderer renderer { get; set; }
 
+        private static Type[] testSkinTypes = new[]
+        {
+            null,
+            typeof(DefaultLegacySkin),
+            typeof(TrianglesSkin),
+            typeof(ArgonSkin),
+            typeof(TestSkin),
+        };
+
+        /// <summary>
+        /// A <see cref="SkinProvidingContainer"/> should always have fallbacks for skin resource lookups.
+        /// This is to allow placeable components from various skin iterations to resolve their resources.
+        /// </summary>
+        [TestCaseSource(nameof(testSkinTypes))]
+        public void TestLegacyTextureFallbackLookups(Type skinType)
+        {
+            ISkin skin = (ISkin)(skinType == null ? null : Activator.CreateInstance(skinType, this));
+
+            SkinProvidingContainer provider = null;
+
+            AddStep("setup sources", () => Child = provider = new SkinProvidingContainer(skin));
+
+            // This resource is used by `LegacyKeyCounterDisplay`.
+            AddAssert("test classic default lookup", () => provider.FindProvider(s => s.GetTexture(@"inputoverlay-background") != null) is DefaultLegacySkin);
+        }
+
         /// <summary>
         /// Ensures that the first inserted skin after resetting (via source change)
         /// is always prioritised over others when providing the same resource.
@@ -59,6 +92,20 @@ public void TestPriorityPreservation()
             });
         }
 
+        #region IResourceStorageProvider
+
+        [Resolved]
+        private GameHost host { get; set; }
+
+        public IRenderer Renderer => host.Renderer;
+        public AudioManager AudioManager => Audio;
+        public IResourceStore<byte[]> Files => null!;
+        public new IResourceStore<byte[]> Resources => base.Resources;
+        public IResourceStore<TextureUpload> CreateTextureLoaderStore(IResourceStore<byte[]> underlyingStore) => host.CreateTextureLoaderStore(underlyingStore);
+        RealmAccess IStorageResourceProvider.RealmAccess => null!;
+
+        #endregion
+
         private partial class TestSkinProvidingContainer : SkinProvidingContainer
         {
             private readonly IEnumerable<ISkin> sources;
@@ -82,12 +129,16 @@ private class TestSkin : ISkin
 
             private readonly IRenderer renderer;
 
+            public TestSkin([CanBeNull] IStorageResourceProvider _)
+            {
+            }
+
             public TestSkin(IRenderer renderer)
             {
                 this.renderer = renderer;
             }
 
-            public Drawable GetDrawableComponent(ISkinComponentLookup lookup) => throw new System.NotImplementedException();
+            public Drawable GetDrawableComponent(ISkinComponentLookup lookup) => throw new NotImplementedException();
 
             public Texture GetTexture(string componentName, WrapMode wrapModeS, WrapMode wrapModeT)
             {
@@ -97,9 +148,9 @@ public Texture GetTexture(string componentName, WrapMode wrapModeS, WrapMode wra
                 return null;
             }
 
-            public ISample GetSample(ISampleInfo sampleInfo) => throw new System.NotImplementedException();
+            public ISample GetSample(ISampleInfo sampleInfo) => throw new NotImplementedException();
 
-            public IBindable<TValue> GetConfig<TLookup, TValue>(TLookup lookup) => throw new System.NotImplementedException();
+            public IBindable<TValue> GetConfig<TLookup, TValue>(TLookup lookup) => throw new NotImplementedException();
         }
     }
 }