Add test for ldm

tests/NATS.Client.Core.Tests/NatsConnectionTest.cs

@@ -505,6 +505,32 @@ public async Task ReconnectOnOpenConnection_ShouldDisconnectAndOpenNewConnection
         openedCount.ShouldBe(1);
         disconnectedCount.ShouldBe(1);
     }
+
+    [Fact]
+    public async Task LameDuckModeActivated_EventHandlerShouldBeInvokedWhenInfoWithLDMRecievied()
+    {
+        // Arrange
+        await using var server = NatsServer.Start(_output, _transportType);
+        await using var connection = server.CreateClientConnection();
+        await connection.ConnectAsync();
+
+        var invocationCount = 0;
+        var ldmSignal = new WaitSignal();
+
+        connection.LameDuckModeActivated += (_, _) =>
+        {
+            Interlocked.Increment(ref invocationCount);
+            ldmSignal.Pulse();
+            return default;
+        };
+
+        // Act
+        server.SignalLameDuckMode();
+        await ldmSignal;
+
+        // Assert
+        invocationCount.ShouldBe(1);
+    }
 }
 
 [JsonSerializable(typeof(SampleClass))]

tests/NATS.Client.TestUtilities/NatsServer.cs

@@ -438,6 +438,34 @@ public void LogMessage<TState>(string categoryName, LogLevel logLevel, EventId e
         }
     }
 
+    public void SignalLameDuckMode()
+    {
+        if (ServerProcess == null || ServerProcess.HasExited)
+        {
+            throw new Exception("Cannot signal LDM, server process is not running.");
+        }
+
+        var signalProcess = new Process
+        {
+            StartInfo = new ProcessStartInfo
+            {
+                FileName = NatsServerPath,
+                Arguments = $"--signal ldm={ServerProcess.Id}",
+                RedirectStandardOutput = true,
+                UseShellExecute = false,
+            }
+        };
+
+        signalProcess.Start();
+        signalProcess.WaitForExit();
+
+        if (signalProcess.ExitCode != 0)
+        {
+            var error = signalProcess.StandardError.ReadToEnd();
+            throw new Exception($"Failed to signal lame duck mode: {error}");
+        }
+    }
+
     private static (string configFileName, string config, string cmd) GetCmd(NatsServerOpts opts)
     {
         var configFileName = Path.GetTempFileName();