Move MockNestedHitObject to own class

osu.Game.Tests/Editing/Checks/MockNestableHitObject.cs

@@ -0,0 +1,36 @@
+// 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.Generic;
+using System.Threading;
+using osu.Game.Rulesets.Objects;
+using osu.Game.Rulesets.Objects.Types;
+
+namespace osu.Game.Tests.Editing.Checks
+{
+    public sealed class MockNestableHitObject : HitObject, IHasDuration
+    {
+        private readonly IEnumerable<HitObject> toBeNested;
+
+        public MockNestableHitObject(IEnumerable<HitObject> toBeNested, double startTime, double endTime)
+        {
+            this.toBeNested = toBeNested;
+            StartTime = startTime;
+            EndTime = endTime;
+        }
+
+        protected override void CreateNestedHitObjects(CancellationToken cancellationToken)
+        {
+            foreach (var hitObject in toBeNested)
+                AddNested(hitObject);
+        }
+
+        public double EndTime { get; }
+
+        public double Duration
+        {
+            get => EndTime - StartTime;
+            set => throw new System.NotImplementedException();
+        }
+    }
+}