2 files changed, 142 insertions, 0 deletions
diff --git a/tests/Jellyfin.Controller.Tests/Entities/InternalItemsQueryTests.cs b/tests/Jellyfin.Controller.Tests/Entities/InternalItemsQueryTests.cs
new file mode 100644
index 000000000..7093b2500
--- /dev/null
+++ b/tests/Jellyfin.Controller.Tests/Entities/InternalItemsQueryTests.cs
@@ -0,0 +1,26 @@
+using System;
+using MediaBrowser.Controller.Entities;
+using MediaBrowser.Model.Querying;
+using Xunit;
+
+namespace Jellyfin.Controller.Tests.Entities;
+
+public class InternalItemsQueryTests
+{
+    public static TheoryData<ItemFilter[]> ApplyFilters_Invalid()
+    {
+        var data = new TheoryData<ItemFilter[]>();
+        data.Add([ItemFilter.IsFolder, ItemFilter.IsNotFolder]);
+        data.Add([ItemFilter.IsPlayed, ItemFilter.IsUnplayed]);
+        data.Add([ItemFilter.Likes, ItemFilter.Dislikes]);
+        return data;
+    }
+
+    [Theory]
+    [MemberData(nameof(ApplyFilters_Invalid))]
+    public void ApplyFilters_Invalid_ThrowsArgumentException(ItemFilter[] filters)
+    {
+        var query = new InternalItemsQuery();
+        Assert.Throws<ArgumentException>(() => query.ApplyFilters(filters));
+    }
+}
diff --git a/tests/Jellyfin.Model.Tests/Extensions/EnumerableExtensionsTests.cs b/tests/Jellyfin.Model.Tests/Extensions/EnumerableExtensionsTests.cs
new file mode 100644
index 000000000..135a139cd
--- /dev/null
+++ b/tests/Jellyfin.Model.Tests/Extensions/EnumerableExtensionsTests.cs
@@ -0,0 +1,116 @@
+using System.Linq;
+using MediaBrowser.Model.Extensions;
+using MediaBrowser.Model.Providers;
+using Xunit;
+
+namespace Jellyfin.Model.Tests.Extensions;
+
+public class EnumerableExtensionsTests
+{
+    [Fact]
+    public void OrderByLanguageDescending_PreferredLanguageFirst()
+    {
+        var images = new[]
+        {
+            new RemoteImageInfo { Language = "en", CommunityRating = 5.0, VoteCount = 100 },
+            new RemoteImageInfo { Language = "de", CommunityRating = 9.0, VoteCount = 200 },
+            new RemoteImageInfo { Language = null, CommunityRating = 7.0, VoteCount = 50 },
+            new RemoteImageInfo { Language = "fr", CommunityRating = 8.0, VoteCount = 150 },
+        };
+
+        var result = images.OrderByLanguageDescending("de").ToList();
+
+        Assert.Equal("de", result[0].Language);
+        Assert.Equal("en", result[1].Language);
+        Assert.Null(result[2].Language);
+        Assert.Equal("fr", result[3].Language);
+    }
+
+    [Fact]
+    public void OrderByLanguageDescending_EnglishBeforeNoLanguage()
+    {
+        var images = new[]
+        {
+            new RemoteImageInfo { Language = null, CommunityRating = 9.0, VoteCount = 500 },
+            new RemoteImageInfo { Language = "en", CommunityRating = 3.0, VoteCount = 10 },
+        };
+
+        var result = images.OrderByLanguageDescending("de").ToList();
+
+        // English should come before no-language, even with lower rating
+        Assert.Equal("en", result[0].Language);
+        Assert.Null(result[1].Language);
+    }
+
+    [Fact]
+    public void OrderByLanguageDescending_SameLanguageSortedByRatingThenVoteCount()
+    {
+        var images = new[]
+        {
+            new RemoteImageInfo { Language = "de", CommunityRating = 5.0, VoteCount = 100 },
+            new RemoteImageInfo { Language = "de", CommunityRating = 9.0, VoteCount = 50 },
+            new RemoteImageInfo { Language = "de", CommunityRating = 9.0, VoteCount = 200 },
+        };
+
+        var result = images.OrderByLanguageDescending("de").ToList();
+
+        Assert.Equal(200, result[0].VoteCount);
+        Assert.Equal(50, result[1].VoteCount);
+        Assert.Equal(100, result[2].VoteCount);
+    }
+
+    [Fact]
+    public void OrderByLanguageDescending_NullRequestedLanguage_DefaultsToEnglish()
+    {
+        var images = new[]
+        {
+            new RemoteImageInfo { Language = "fr", CommunityRating = 9.0, VoteCount = 500 },
+            new RemoteImageInfo { Language = "en", CommunityRating = 5.0, VoteCount = 10 },
+        };
+
+        var result = images.OrderByLanguageDescending(null!).ToList();
+
+        // With null requested language, English becomes the preferred language (score 4)
+        Assert.Equal("en", result[0].Language);
+        Assert.Equal("fr", result[1].Language);
+    }
+
+    [Fact]
+    public void OrderByLanguageDescending_EnglishRequested_NoDoubleBoost()
+    {
+        // When requested language IS English, "en" gets score 4 (requested match),
+        // no-language gets score 2, others get score 0
+        var images = new[]
+        {
+            new RemoteImageInfo { Language = null, CommunityRating = 9.0, VoteCount = 500 },
+            new RemoteImageInfo { Language = "en", CommunityRating = 3.0, VoteCount = 10 },
+            new RemoteImageInfo { Language = "fr", CommunityRating = 8.0, VoteCount = 300 },
+        };
+
+        var result = images.OrderByLanguageDescending("en").ToList();
+
+        Assert.Equal("en", result[0].Language);
+        Assert.Null(result[1].Language);
+        Assert.Equal("fr", result[2].Language);
+    }
+
+    [Fact]
+    public void OrderByLanguageDescending_FullPriorityOrder()
+    {
+        var images = new[]
+        {
+            new RemoteImageInfo { Language = "fr", CommunityRating = 9.0, VoteCount = 500 },
+            new RemoteImageInfo { Language = null, CommunityRating = 8.0, VoteCount = 400 },
+            new RemoteImageInfo { Language = "en", CommunityRating = 7.0, VoteCount = 300 },
+            new RemoteImageInfo { Language = "de", CommunityRating = 6.0, VoteCount = 200 },
+        };
+
+        var result = images.OrderByLanguageDescending("de").ToList();
+
+        // Expected order: de (requested) > en > no-language > fr (other)
+        Assert.Equal("de", result[0].Language);
+        Assert.Equal("en", result[1].Language);
+        Assert.Null(result[2].Language);
+        Assert.Equal("fr", result[3].Language);
+    }
+}