add test case list helper for testing time-tag with random state.

osu.Game.Rulesets.Karaoke.Tests/Helper/TestCaseListHelper.cs

@@ -0,0 +1,26 @@
+// Copyright (c) andy840119 <[email protected]>. Licensed under the GPL Licence.
+// See the LICENCE file in the repository root for full licence text.
+
+using System;
+using System.Collections.Generic;
+using System.Linq;
+
+namespace osu.Game.Rulesets.Karaoke.Tests.Helper
+{
+    public static class TestCaseListHelper
+    {
+        private static readonly Random rng = new();
+
+        /// <summary>
+        /// Random the order of the list.
+        /// </summary>
+        /// <param name="list"></param>
+        /// <typeparam name="T"></typeparam>
+        /// <returns></returns>
+        public static IList<T> Shuffle<T>(IList<T> list)
+        {
+            // see: https://stackoverflow.com/a/4262134
+            return list.OrderBy(_ => rng.Next()).ToList();
+        }
+    }
+}