Add test checking incompatibility of multi mods

osu.Game.Tests/Mods/MultiModIncompatibilityTest.cs

@@ -0,0 +1,65 @@
+// 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;
+using System.Collections.Generic;
+using System.Linq;
+using NUnit.Framework;
+using osu.Game.Rulesets;
+using osu.Game.Rulesets.Catch;
+using osu.Game.Rulesets.Mania;
+using osu.Game.Rulesets.Mods;
+using osu.Game.Rulesets.Osu;
+using osu.Game.Rulesets.Taiko;
+using osu.Game.Utils;
+
+namespace osu.Game.Tests.Mods
+{
+    [TestFixture]
+    public class MultiModIncompatibilityTest
+    {
+        /// <summary>
+        /// Ensures that all mods grouped into <see cref="MultiMod"/>s, as declared by the default rulesets, are pairwise incompatible with each other.
+        /// </summary>
+        [TestCase(typeof(OsuRuleset))]
+        [TestCase(typeof(TaikoRuleset))]
+        [TestCase(typeof(CatchRuleset))]
+        [TestCase(typeof(ManiaRuleset))]
+        public void TestAllMultiModsFromRulesetAreIncompatible(Type rulesetType)
+        {
+            var ruleset = (Ruleset)Activator.CreateInstance(rulesetType);
+            Assert.That(ruleset, Is.Not.Null);
+
+            var allMultiMods = getMultiMods(ruleset);
+
+            Assert.Multiple(() =>
+            {
+                foreach (var multiMod in allMultiMods)
+                {
+                    int modCount = multiMod.Mods.Length;
+
+                    for (int i = 0; i < modCount; ++i)
+                    {
+                        // indexing from i + 1 ensures that only pairs of different mods are checked, and are checked only once
+                        // (indexing from 0 would check each pair twice, and also check each mod against itself).
+                        for (int j = i + 1; j < modCount; ++j)
+                        {
+                            var firstMod = multiMod.Mods[i];
+                            var secondMod = multiMod.Mods[j];
+
+                            Assert.That(
+                                ModUtils.CheckCompatibleSet(new[] { firstMod, secondMod }), Is.False,
+                                $"{firstMod.Name} ({firstMod.Acronym}) and {secondMod.Name} ({secondMod.Acronym}) should be incompatible.");
+                        }
+                    }
+                }
+            });
+        }
+
+        /// <remarks>
+        /// This local helper is used rather than <see cref="Ruleset.CreateAllMods"/>, because the aforementioned method flattens multi mods.
+        /// </remarks>>
+        private static IEnumerable<MultiMod> getMultiMods(Ruleset ruleset)
+            => Enum.GetValues(typeof(ModType)).Cast<ModType>().SelectMany(ruleset.GetModsFor).OfType<MultiMod>();
+    }
+}