From f642546d6a385be54181138ce868a3df80d28950 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Bart=C5=82omiej=20Dach?= <dach.bartlomiej@gmail.com>
Date: Sat, 21 Aug 2021 15:15:13 +0200
Subject: [PATCH] Add failing test case

---
 .../TestSceneBeatmapDifficultyCache.cs        | 23 +++++++++++++++++++
 1 file changed, 23 insertions(+)

diff --git a/osu.Game.Tests/Beatmaps/TestSceneBeatmapDifficultyCache.cs b/osu.Game.Tests/Beatmaps/TestSceneBeatmapDifficultyCache.cs
index 7bbe647302..2b4dc48fe0 100644
--- a/osu.Game.Tests/Beatmaps/TestSceneBeatmapDifficultyCache.cs
+++ b/osu.Game.Tests/Beatmaps/TestSceneBeatmapDifficultyCache.cs
@@ -74,6 +74,29 @@ namespace osu.Game.Tests.Beatmaps
             AddUntilStep($"star difficulty -> {BASE_STARS + 1.75}", () => starDifficultyBindable.Value?.Stars == BASE_STARS + 1.75);
         }
 
+        [Test]
+        public void TestStarDifficultyAdjustHashCodeConflict()
+        {
+            OsuModDifficultyAdjust difficultyAdjust = null;
+
+            AddStep("set computation function", () => difficultyCache.ComputeDifficulty = lookup =>
+            {
+                var modDifficultyAdjust = (ModDifficultyAdjust)lookup.OrderedMods.SingleOrDefault(mod => mod is ModDifficultyAdjust);
+                return new StarDifficulty(BASE_STARS * (modDifficultyAdjust?.OverallDifficulty.Value ?? 1), 0);
+            });
+
+            AddStep("change selected mod to DA", () => SelectedMods.Value = new[] { difficultyAdjust = new OsuModDifficultyAdjust() });
+            AddUntilStep($"star difficulty -> {BASE_STARS}", () => starDifficultyBindable.Value?.Stars == BASE_STARS);
+
+            AddStep("change DA difficulty to 0.5", () => difficultyAdjust.OverallDifficulty.Value = 0.5f);
+            AddUntilStep($"star difficulty -> {BASE_STARS * 0.5f}", () => starDifficultyBindable.Value?.Stars == BASE_STARS / 2);
+
+            // hash code of 0 (the value) conflicts with the hash code of null (the initial/default value).
+            // it's important that the mod reference and its underlying bindable references stay the same to demonstrate this failure.
+            AddStep("change DA difficulty to 0", () => difficultyAdjust.OverallDifficulty.Value = 0);
+            AddUntilStep($"star difficulty -> 0", () => starDifficultyBindable.Value?.Stars == 0);
+        }
+
         [Test]
         public void TestKeyEqualsWithDifferentModInstances()
         {