test(session): prove the directory and bus fall back together

tests/Jellyfin.Server.Tests/HighAvailability/SessionDirectoryRegistrationTests.cs

@@ -5,6 +5,8 @@ using MediaBrowser.Controller.Session;
 using Microsoft.Extensions.Configuration;
 using Microsoft.Extensions.DependencyInjection;
 using Microsoft.Extensions.Logging.Abstractions;
+using Moq;
+using StackExchange.Redis;
 using Xunit;
 
 namespace Jellyfin.Server.Tests.HighAvailability;
@@ -25,16 +27,21 @@ public static class SessionDirectoryRegistrationTests
     }
 
     [Fact]
-    public static void AddSessionDirectory_WithAnUnusableRedisConnection_FallsBackOnBothHalves()
+    public static void AddSessionDirectory_WhenOneHalfCannotBeBuilt_FallsBackOnBoth()
     {
-        // The multiplexer is deliberately absent, which is what an unreachable Redis amounts to here.
-        var services = Build(configured: true);
+        // A connection that can serve the directory but not the bus: taking the directory on its own
+        // would advertise every instance's sessions and then fail every command sent to one.
+        var redis = new Mock<IConnectionMultiplexer>();
+        redis.Setup(i => i.GetDatabase(It.IsAny<int>(), It.IsAny<object>())).Returns(Mock.Of<IDatabase>());
+        redis.Setup(i => i.GetSubscriber(It.IsAny<object>())).Throws(new RedisConnectionException(ConnectionFailureType.UnableToConnect, "unreachable"));
+
+        var services = Build(configured: true, redis.Object);
 
         Assert.IsType<NullSessionDirectory>(services.GetRequiredService<ISessionDirectory>());
         Assert.IsType<NullPodMessageBus>(services.GetRequiredService<IPodMessageBus>());
     }
 
-    private static ServiceProvider Build(bool configured)
+    private static ServiceProvider Build(bool configured, IConnectionMultiplexer? redis = null)
     {
         var settings = new Dictionary<string, string?>();
         if (configured)
@@ -43,9 +50,14 @@ public static class SessionDirectoryRegistrationTests
         }
 
         var configuration = new ConfigurationBuilder().AddInMemoryCollection(settings).Build();
+        var serviceCollection = new ServiceCollection().AddLogging();
 
-        return new ServiceCollection()
-            .AddLogging()
+        if (redis is not null)
+        {
+            serviceCollection.AddSingleton(redis);
+        }
+
+        return serviceCollection
             .AddSessionDirectory(configuration, NullLogger.Instance)
             .BuildServiceProvider();
     }