refactor: rename remaining tests to NATS.Server.Core.Tests

- Rename tests/NATS.Server.Tests -> tests/NATS.Server.Core.Tests
- Update solution file, InternalsVisibleTo, and csproj references
- Remove JETSTREAM_INTEGRATION_MATRIX and NATS.NKeys from csproj (moved to JetStream.Tests and Auth.Tests)
- Update all namespaces from NATS.Server.Tests.* to NATS.Server.Core.Tests.*
- Replace private GetFreePort/ReadUntilAsync helpers with TestUtilities calls
- Fix stale namespace in Transport.Tests/NetworkingGoParityTests.cs

tests/NATS.Server.Core.Tests/ServerConfigTests.cs

@@ -0,0 +1,139 @@
+using System.Net;
+using System.Net.Sockets;
+using System.Text;
+using Microsoft.Extensions.Logging.Abstractions;
+using NATS.Server;
+using NATS.Server.TestUtilities;
+
+namespace NATS.Server.Core.Tests;
+
+// Tests ported from Go server_test.go:
+//   TestRandomPorts, TestInfoServerNameDefaultsToPK, TestInfoServerNameIsSettable,
+//   TestLameDuckModeInfo (simplified — no cluster, just ldm property/state)
+public class ServerConfigTests
+{
+
+
+    // Ref: golang/nats-server/server/server_test.go TestRandomPorts
+    // The Go test uses Port=-1 (their sentinel for "random"), we use Port=0 (.NET/BSD standard).
+    // Verifies that after startup, server.Port is resolved to a non-zero ephemeral port.
+    [Fact]
+    public async Task Server_resolves_ephemeral_port_when_zero()
+    {
+        var opts = new NatsOptions { Port = 0 };
+        using var server = new NatsServer(opts, NullLoggerFactory.Instance);
+        using var cts = new CancellationTokenSource();
+
+        _ = server.StartAsync(cts.Token);
+        await server.WaitForReadyAsync();
+
+        try
+        {
+            server.Port.ShouldBeGreaterThan(0);
+            server.Port.ShouldNotBe(4222);
+        }
+        finally
+        {
+            await cts.CancelAsync();
+        }
+    }
+
+    // Ref: golang/nats-server/server/server_test.go TestInfoServerNameIsSettable
+    // Verifies that ServerName set in options is reflected in both the server property
+    // and the INFO line sent to connecting clients.
+    [Fact]
+    public async Task Server_info_contains_server_name()
+    {
+        const string name = "my-test-server";
+        var port = TestPortAllocator.GetFreePort();
+        var opts = new NatsOptions { Port = port, ServerName = name };
+        using var server = new NatsServer(opts, NullLoggerFactory.Instance);
+        using var cts = new CancellationTokenSource();
+
+        _ = server.StartAsync(cts.Token);
+        await server.WaitForReadyAsync();
+
+        try
+        {
+            // Property check
+            server.ServerName.ShouldBe(name);
+
+            // Wire check — INFO line sent on connect
+            using var sock = new Socket(AddressFamily.InterNetwork, SocketType.Stream, ProtocolType.Tcp);
+            await sock.ConnectAsync(IPAddress.Loopback, port);
+            var infoLine = await SocketTestHelper.ReadUntilAsync(sock, "INFO");
+            infoLine.ShouldContain("\"server_name\":\"my-test-server\"");
+        }
+        finally
+        {
+            await cts.CancelAsync();
+        }
+    }
+
+    // Ref: golang/nats-server/server/server_test.go TestInfoServerNameDefaultsToPK
+    // Verifies that when no ServerName is configured, the server still populates both
+    // server_id and server_name fields in the INFO line (name defaults to a generated value,
+    // not null or empty).
+    [Fact]
+    public async Task Server_info_defaults_name_when_not_configured()
+    {
+        var port = TestPortAllocator.GetFreePort();
+        var opts = new NatsOptions { Port = port };  // no ServerName set
+        using var server = new NatsServer(opts, NullLoggerFactory.Instance);
+        using var cts = new CancellationTokenSource();
+
+        _ = server.StartAsync(cts.Token);
+        await server.WaitForReadyAsync();
+
+        try
+        {
+            // Both properties should be populated
+            server.ServerId.ShouldNotBeNullOrWhiteSpace();
+            server.ServerName.ShouldNotBeNullOrWhiteSpace();
+
+            // Wire check — INFO line includes both fields
+            using var sock = new Socket(AddressFamily.InterNetwork, SocketType.Stream, ProtocolType.Tcp);
+            await sock.ConnectAsync(IPAddress.Loopback, port);
+            var infoLine = await SocketTestHelper.ReadUntilAsync(sock, "INFO");
+            infoLine.ShouldContain("\"server_id\":");
+            infoLine.ShouldContain("\"server_name\":");
+        }
+        finally
+        {
+            await cts.CancelAsync();
+        }
+    }
+
+    // Ref: golang/nats-server/server/server_test.go TestLameDuckModeInfo
+    // Simplified port: verifies that LameDuckShutdownAsync transitions the server into
+    // lame duck mode (IsLameDuckMode becomes true) and that the server ultimately shuts
+    // down. The full Go test requires a cluster to observe INFO updates with "ldm":true;
+    // that aspect is not ported here because the .NET ServerInfo type does not include
+    // an ldm/LameDuckMode field and cluster routing is out of scope for this test.
+    [Fact]
+    public async Task Lame_duck_mode_sets_is_lame_duck_mode_and_shuts_down()
+    {
+        var port = TestPortAllocator.GetFreePort();
+        var opts = new NatsOptions
+        {
+            Port = port,
+            LameDuckGracePeriod = TimeSpan.Zero,
+            LameDuckDuration = TimeSpan.FromMilliseconds(50),
+        };
+        using var server = new NatsServer(opts, NullLoggerFactory.Instance);
+        using var cts = new CancellationTokenSource();
+
+        _ = server.StartAsync(cts.Token);
+        await server.WaitForReadyAsync();
+
+        server.IsLameDuckMode.ShouldBeFalse();
+
+        // Trigger lame duck — no clients connected so it should proceed straight to shutdown.
+        await server.LameDuckShutdownAsync();
+
+        server.IsLameDuckMode.ShouldBeTrue();
+        server.IsShuttingDown.ShouldBeTrue();
+
+        await cts.CancelAsync();
+    }
+}