1 files changed, 117 insertions, 0 deletions
diff --git a/tests/Jellyfin.Server.Implementations.Tests/Library/PeopleValidatorPartitionTests.cs b/tests/Jellyfin.Server.Implementations.Tests/Library/PeopleValidatorPartitionTests.cs
new file mode 100644
index 0000000000..30f7bed208
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+++ b/tests/Jellyfin.Server.Implementations.Tests/Library/PeopleValidatorPartitionTests.cs
@@ -0,0 +1,117 @@
+using System;
+using System.Collections.Generic;
+using Emby.Server.Implementations.Library.Validators;
+using Xunit;
+
+namespace Jellyfin.Server.Implementations.Tests.Library;
+
+/// <summary>
+/// Tests for how the people validator decides which credits need a person item and which person items
+/// nothing credits any more. Keying either half on the item's name rather than its id put the two halves
+/// in a loop that created, refreshed and deleted the same people on every run, so these pin the id.
+/// </summary>
+public class PeopleValidatorPartitionTests
+{
+    // Stands in for the real item-by-name id: derived from the credit name, case-insensitively, and
+    // from nothing else. The property that matters is that it does not depend on the item's own name.
+    private static Guid PersonId(string creditName)
+    {
+#pragma warning disable CA5351 // Do Not Use Broken Cryptographic Algorithms
+        var hash = System.Security.Cryptography.MD5.HashData(
+            System.Text.Encoding.Unicode.GetBytes(creditName.ToLowerInvariant()));
+#pragma warning restore CA5351 // Do Not Use Broken Cryptographic Algorithms
+        return new Guid(hash);
+    }
+
+    [Fact]
+    public void PartitionCreditsByPersonId_ProviderRenamedThePerson_KeepsThemAndCreatesNothing()
+    {
+        // The credit still says "AURORA"; the item it made has been renamed to "Aurora" by the provider
+        // that refreshed it. Nothing about the library changed, so nothing should be created or deleted.
+        var credits = new[] { "AURORA" };
+        var existing = new HashSet<Guid> { PersonId("AURORA") };
+
+        var (newNames, deadIds) = PeopleValidator.PartitionCreditsByPersonId(credits, PersonId, existing);
+
+        Assert.Empty(newNames);
+        Assert.Empty(deadIds);
+    }
+
+    [Theory]
+    // Every shape of rename seen in the wild on a real library.
+    [InlineData("AURORA")]
+    [InlineData("Amir AboulEla")]
+    [InlineData("Miguel Ángel Fuentes")]
+    [InlineData("a‐ha")]
+    [InlineData("윤현민")]
+    public void PartitionCreditsByPersonId_CreditWithAnItem_IsNeverBothCreatedAndDeleted(string creditName)
+    {
+        var existing = new HashSet<Guid> { PersonId(creditName) };
+
+        var (newNames, deadIds) = PeopleValidator.PartitionCreditsByPersonId([creditName], PersonId, existing);
+
+        Assert.Empty(newNames);
+        Assert.Empty(deadIds);
+    }
+
+    [Fact]
+    public void PartitionCreditsByPersonId_CreditWithNoItem_IsCreated()
+    {
+        var (newNames, deadIds) = PeopleValidator.PartitionCreditsByPersonId(
+            ["Wanted Person"],
+            PersonId,
+            new HashSet<Guid>());
+
+        Assert.Equal(["Wanted Person"], newNames);
+        Assert.Empty(deadIds);
+    }
+
+    [Fact]
+    public void PartitionCreditsByPersonId_ItemNoCreditNames_IsDead()
+    {
+        var orphan = PersonId("Nobody Credits Me");
+        var existing = new HashSet<Guid> { PersonId("Credited"), orphan };
+
+        var (newNames, deadIds) = PeopleValidator.PartitionCreditsByPersonId(["Credited"], PersonId, existing);
+
+        Assert.Empty(newNames);
+        Assert.Equal([orphan], deadIds);
+    }
+
+    [Fact]
+    public void PartitionCreditsByPersonId_CreditsNormalizingOntoOneId_CreateOneItem()
+    {
+        // "AURORA" and "Aurora" are one person as far as the item-by-name id is concerned, so exactly
+        // one of them should create the item and neither should end up dead.
+        var (newNames, deadIds) = PeopleValidator.PartitionCreditsByPersonId(
+            ["AURORA", "Aurora", "aurora"],
+            PersonId,
+            new HashSet<Guid>());
+
+        Assert.Single(newNames);
+        Assert.Empty(deadIds);
+    }
+
+    [Fact]
+    public void PartitionCreditsByPersonId_SecondRunAfterCreating_AsksForNothingFurther()
+    {
+        // The churn showed up as a run that never settled, so drive two rounds: whatever round one
+        // created must leave round two with nothing to do.
+        string[] credits = ["AURORA", "Amir AboulEla", "Miguel Ángel Fuentes"];
+        var existing = new HashSet<Guid>();
+
+        var (firstNames, firstDead) = PeopleValidator.PartitionCreditsByPersonId(credits, PersonId, existing);
+        Assert.Equal(3, firstNames.Count);
+        Assert.Empty(firstDead);
+
+        foreach (var created in firstNames)
+        {
+            existing.Add(PersonId(created));
+        }
+
+        var (secondNames, secondDead) = PeopleValidator.PartitionCreditsByPersonId(credits, PersonId, existing);
+
+        Assert.Empty(secondNames);
+        Assert.Empty(secondDead);
+    }
+}