Actually make ManiaHitObjectComposer constructible/testable

osu.Game.Rulesets.Mania.Tests/TestCaseEditor.cs

@@ -0,0 +1,17 @@
+// Copyright (c) 2007-2018 ppy Pty Ltd <contact@ppy.sh>.
+// Licensed under the MIT Licence - https://raw.githubusercontent.com/ppy/osu/master/LICENCE
+
+using NUnit.Framework;
+using osu.Game.Tests.Visual;
+
+namespace osu.Game.Rulesets.Mania.Tests
+{
+    [TestFixture]
+    public class TestCaseEditor : EditorTestCase
+    {
+        public TestCaseEditor()
+            : base(new ManiaRuleset())
+        {
+        }
+    }
+}