Add catch difficulty calculator tests

osu.Game.Rulesets.Catch.Tests/CatchDifficultyCalculatorTest.cs

@@ -0,0 +1,24 @@
+// 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 NUnit.Framework;
+using osu.Game.Beatmaps;
+using osu.Game.Rulesets.Catch.Difficulty;
+using osu.Game.Rulesets.Difficulty;
+using osu.Game.Tests.Beatmaps;
+
+namespace osu.Game.Rulesets.Catch.Tests
+{
+    public class CatchDifficultyCalculatorTest : DifficultyCalculatorTest
+    {
+        protected override string ResourceAssembly => "osu.Game.Rulesets.Catch";
+
+        [TestCase(3.8664391043534758, "diffcalc-test")]
+        public void Test(double expected, string name)
+            => base.Test(expected, name);
+
+        protected override DifficultyCalculator CreateDifficultyCalculator(WorkingBeatmap beatmap) => new CatchDifficultyCalculator(new CatchRuleset(), beatmap);
+
+        protected override Ruleset CreateRuleset() => new CatchRuleset();
+    }
+}