Add osu! difficulty calculator test

osu.Game.Rulesets.Osu.Tests/OsuDifficultyCalculatorTest.cs

@@ -0,0 +1,32 @@
+// 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.Diagnostics;
+using NUnit.Framework;
+using osu.Game.Beatmaps;
+using osu.Game.Rulesets.Difficulty;
+using osu.Game.Rulesets.Osu.Difficulty;
+using osu.Game.Tests.Beatmaps;
+
+namespace osu.Game.Rulesets.Osu.Tests
+{
+    [TestFixture]
+    public class OsuDifficultyCalculatorTest : DifficultyCalculatorTest
+    {
+        protected override string ResourceAssembly => "osu.Game.Rulesets.Osu";
+
+        [Test]
+        public new void Test()
+        {
+            base.Test(6.9311449688341344, "diffcalc-test");
+        }
+
+        private void openUsingShellExecute(string path) => Process.Start(new ProcessStartInfo
+        {
+            FileName = path,
+            UseShellExecute = true //see https://github.com/dotnet/corefx/issues/10361
+        });
+
+        protected override DifficultyCalculator CreateDifficultyCalculator(WorkingBeatmap beatmap) => new OsuDifficultyCalculator(new OsuRuleset(), beatmap);
+    }
+}