Add test implementation of the ruleset config cache

osu.Game/Tests/Rulesets/TestRulesetConfigCache.cs

@@ -0,0 +1,19 @@
+// 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.Collections.Concurrent;
+using osu.Game.Rulesets;
+using osu.Game.Rulesets.Configuration;
+
+namespace osu.Game.Tests.Rulesets
+{
+    /// <summary>
+    /// Test implementation of a <see cref="IRulesetConfigCache"/>, which ensures isolation between test scenes.
+    /// </summary>
+    public class TestRulesetConfigCache : IRulesetConfigCache
+    {
+        private readonly ConcurrentDictionary<string, IRulesetConfigManager> configCache = new ConcurrentDictionary<string, IRulesetConfigManager>();
+
+        public IRulesetConfigManager GetConfigFor(Ruleset ruleset) => configCache.GetOrAdd(ruleset.ShortName, _ => ruleset.CreateConfig(null));
+    }
+}