Music never falls silent (TrackPicker); mod unit tests

manifest.json

@@ -8,6 +8,7 @@
   "sources": [
     "src/**/*.cs"
   ],
+  "test_sources": ["tests/*.cs"],
   "depends": ["shell2d_base>=1", "ui_base>=1"],
   "ui": []
 }

src/MusicPlayerBehaviour.cs

@@ -276,24 +276,11 @@ namespace Cthangover.Mods.Audio
             if (dict == null || !dict.TryGetValue(playlistContext.LastMusicType, out var list) || Lists.IsEmpty(list))
                 return;
 
-            int iteration = 0;
-            for (;;)
-            {
-                int index = (int)(GD.Randi() % (uint)list.Count);
-                var nextMusic = list[index];
+            var nextMusic = TrackPicker.Next(list, playlistContext.LastMusicName, System.Random.Shared);
+            GameLogger.Log("AUDIO", $"NextSound -> '{nextMusic}' (type={playlistContext.LastMusicType}, scene={playlistContext.Playlist?.Scene})");
 
-                if (list.Count == 1 || playlistContext.LastMusicName != nextMusic)
-                {
-                    GameLogger.Log("AUDIO", $"NextSound -> '{nextMusic}' (type={playlistContext.LastMusicType}, scene={playlistContext.Playlist?.Scene})");
-
-                    StopMusic();
-                    PlayMusic(nextMusic);
-                    break;
-                }
-
-                if (iteration++ > 10)
-                    break;
-            }
+            StopMusic();
+            PlayMusic(nextMusic);
         }
 
         /// <summary>

src/TrackPicker.cs

@@ -0,0 +1,31 @@
+using System;
+using System.Collections.Generic;
+
+namespace Cthangover.Mods.Audio
+{
+    /// <summary>
+    /// Picks the next track of a music bucket: a random one different from the
+    /// last played when the bucket offers another, otherwise the last one
+    /// again. Choosing among the other tracks directly — instead of rerolling
+    /// until the pick differs — cannot give up and leave the player silent
+    /// (a bucket holding copies of one track exhausted every reroll).
+    /// </summary>
+    public static class TrackPicker
+    {
+        /// <summary>The next track of <paramref name="tracks"/>, or null for an empty bucket.</summary>
+        public static string Next(IReadOnlyList<string> tracks, string last, Random random)
+        {
+            if (tracks == null || tracks.Count == 0)
+                return null;
+
+            var others = new List<string>();
+            foreach (var track in tracks)
+            {
+                if (track != last)
+                    others.Add(track);
+            }
+
+            return others.Count > 0 ? others[random.Next(others.Count)] : tracks[0];
+        }
+    }
+}

tests/TrackPickerTests.cs

@@ -0,0 +1,27 @@
+namespace Cthangover.Mods.Audio.Tests
+{
+    using System;
+    using System.Collections.Generic;
+    using Cthangover.Core.Mods.Testing;
+
+    /// <summary>
+    /// Choosing the next track never fails: it avoids repeating the last one
+    /// when anything else is available, and a bucket made of one track (or of
+    /// copies of it) still plays instead of falling silent.
+    /// </summary>
+    public class TrackPickerTests
+    {
+        [ModTest("music/next_track_avoids_repeat_and_never_gives_up")]
+        static void NextTrackAvoidsRepeat(ModTestContext ctx)
+        {
+            var random = new Random(3);
+            var list = new List<string> { "a", "b" };
+            for (var i = 0; i < 200; i++)
+                ModAssert.Equal("b", TrackPicker.Next(list, "a", random), "the other track");
+
+            ModAssert.Equal("a", TrackPicker.Next(new List<string> { "a", "a", "a" }, "a", random), "copies of one track still play");
+            ModAssert.Equal("a", TrackPicker.Next(new List<string> { "a" }, "a", random), "a single track repeats");
+            ModAssert.Null(TrackPicker.Next(new List<string>(), "a", random), "an empty bucket gives nothing");
+        }
+    }
+}