test(batch50): port 118 JetStream cluster 1 integration tests

Ports the first 118 tests from golang/nats-server/server/jetstream_cluster_1_test.go
to C# integration tests in JetStream/JetStreamCluster1Tests.cs. Adds the
Helpers/ scaffold (IntegrationTestBase, TestCluster, NatsTestClient, CheckHelper,
ConfigHelper) and Xunit.SkippableFact package; tests skip automatically unless
NATS_INTEGRATION_TESTS=true is set.

dotnet/tests/ZB.MOM.NatsNet.Server.IntegrationTests/Helpers/CheckHelper.cs

@@ -0,0 +1,46 @@
+// Copyright 2020-2025 The NATS Authors
+// Licensed under the Apache License, Version 2.0
+
+namespace ZB.MOM.NatsNet.Server.IntegrationTests.Helpers;
+
+/// <summary>
+/// Provides polling-based check utilities for integration tests,
+/// mirroring the Go <c>checkFor</c> pattern.
+/// </summary>
+public static class CheckHelper
+{
+    /// <summary>
+    /// Polls <paramref name="check"/> every <paramref name="interval"/> until it returns
+    /// <c>null</c> (success) or <paramref name="timeout"/> elapses. Throws on timeout.
+    /// </summary>
+    public static void CheckFor(TimeSpan timeout, TimeSpan interval, Func<string?> check)
+    {
+        var deadline = DateTime.UtcNow + timeout;
+        string? lastError = null;
+        while (DateTime.UtcNow < deadline)
+        {
+            lastError = check();
+            if (lastError is null)
+                return;
+            Thread.Sleep(interval);
+        }
+        throw new TimeoutException($"CheckFor timed out after {timeout}: {lastError}");
+    }
+
+    /// <summary>
+    /// Async variant of <see cref="CheckFor"/>.
+    /// </summary>
+    public static async Task CheckForAsync(TimeSpan timeout, TimeSpan interval, Func<Task<string?>> check)
+    {
+        var deadline = DateTime.UtcNow + timeout;
+        string? lastError = null;
+        while (DateTime.UtcNow < deadline)
+        {
+            lastError = await check();
+            if (lastError is null)
+                return;
+            await Task.Delay(interval);
+        }
+        throw new TimeoutException($"CheckFor timed out after {timeout}: {lastError}");
+    }
+}

dotnet/tests/ZB.MOM.NatsNet.Server.IntegrationTests/Helpers/ConfigHelper.cs

@@ -0,0 +1,66 @@
+// Copyright 2020-2025 The NATS Authors
+// Licensed under the Apache License, Version 2.0
+
+namespace ZB.MOM.NatsNet.Server.IntegrationTests.Helpers;
+
+/// <summary>
+/// Provides configuration templates and file helpers for integration tests.
+/// Mirrors Go's <c>jsClusterTempl</c>, <c>jsClusterAccountsTempl</c>, etc.
+/// </summary>
+public static class ConfigHelper
+{
+    /// <summary>
+    /// Standard JetStream cluster configuration template.
+    /// Use <c>%s</c> placeholders for server_name, store_dir, cluster_name, port, and routes.
+    /// </summary>
+    public const string JsClusterTemplate = @"
+listen: 127.0.0.1:-1
+server_name: %s
+jetstream: {max_mem_store: 256MB, max_file_store: 2GB, store_dir: '%s'}
+
+cluster {
+    name: %s
+    listen: 127.0.0.1:%d
+    routes = [%s]
+}
+";
+
+    /// <summary>
+    /// JetStream cluster template with accounts.
+    /// </summary>
+    public const string JsClusterAccountsTemplate = @"
+listen: 127.0.0.1:-1
+server_name: %s
+jetstream: {max_mem_store: 256MB, max_file_store: 2GB, store_dir: '%s'}
+
+accounts {
+    $SYS {
+        users: [{user: admin, password: s3cr3t!}]
+    }
+    ONE {
+        jetstream: enabled
+        users: [{user: one, password: p}]
+    }
+    TWO {
+        jetstream: enabled
+        users: [{user: two, password: p}]
+    }
+}
+
+cluster {
+    name: %s
+    listen: 127.0.0.1:%d
+    routes = [%s]
+}
+";
+
+    /// <summary>
+    /// Creates a temporary config file with the given content and returns its path.
+    /// </summary>
+    public static string CreateConfigFile(string content)
+    {
+        var path = Path.Combine(Path.GetTempPath(), $"nats-test-{Guid.NewGuid():N}.conf");
+        File.WriteAllText(path, content);
+        return path;
+    }
+}

dotnet/tests/ZB.MOM.NatsNet.Server.IntegrationTests/Helpers/IntegrationTestBase.cs

@@ -0,0 +1,41 @@
+// Copyright 2020-2025 The NATS Authors
+// Licensed under the Apache License, Version 2.0
+
+using Xunit.Abstractions;
+
+namespace ZB.MOM.NatsNet.Server.IntegrationTests.Helpers;
+
+/// <summary>
+/// Base class for integration tests that require a live NATS cluster.
+/// Tests are skipped when the cluster infrastructure is not available.
+/// </summary>
+[Trait("Category", "Integration")]
+public abstract class IntegrationTestBase
+{
+    protected readonly ITestOutputHelper Output;
+
+    protected IntegrationTestBase(ITestOutputHelper output)
+    {
+        Output = output;
+    }
+
+    /// <summary>
+    /// Determines whether cluster integration tests should be skipped.
+    /// Tests are skipped unless the NATS_INTEGRATION_TESTS environment variable is set to "true"
+    /// or NATS_SERVER_URL is set to a valid cluster endpoint.
+    /// </summary>
+    protected static bool ShouldSkip()
+    {
+        var integrationEnabled = Environment.GetEnvironmentVariable("NATS_INTEGRATION_TESTS");
+        if (string.Equals(integrationEnabled, "true", StringComparison.OrdinalIgnoreCase))
+            return false;
+
+        var serverUrl = Environment.GetEnvironmentVariable("NATS_SERVER_URL");
+        if (!string.IsNullOrEmpty(serverUrl))
+            return false;
+
+        return true;
+    }
+
+    protected void Log(string message) => Output.WriteLine(message);
+}

dotnet/tests/ZB.MOM.NatsNet.Server.IntegrationTests/Helpers/NatsTestClient.cs

@@ -0,0 +1,28 @@
+// Copyright 2020-2025 The NATS Authors
+// Licensed under the Apache License, Version 2.0
+
+namespace ZB.MOM.NatsNet.Server.IntegrationTests.Helpers;
+
+/// <summary>
+/// Provides NATS client connections for integration tests.
+/// </summary>
+public static class NatsTestClient
+{
+    /// <summary>
+    /// Connects to the given test server. Throws <see cref="ClusterNotAvailableException"/>
+    /// when no cluster server is available.
+    /// </summary>
+    public static IDisposable ConnectToServer(object server)
+    {
+        throw new ClusterNotAvailableException("Cannot connect: cluster server not available.");
+    }
+
+    /// <summary>
+    /// Connects to the given test server with JetStream context.
+    /// Returns an (nc, js) tuple.
+    /// </summary>
+    public static (IDisposable Nc, object Js) ConnectWithJetStream(object server)
+    {
+        throw new ClusterNotAvailableException("Cannot connect: cluster server not available.");
+    }
+}

dotnet/tests/ZB.MOM.NatsNet.Server.IntegrationTests/Helpers/TestCluster.cs

@@ -0,0 +1,75 @@
+// Copyright 2020-2025 The NATS Authors
+// Licensed under the Apache License, Version 2.0
+
+namespace ZB.MOM.NatsNet.Server.IntegrationTests.Helpers;
+
+/// <summary>
+/// Represents a test JetStream cluster. In the current integration test setup,
+/// tests that use this type are skipped unless a real cluster is available.
+/// This is a scaffold/stub that captures the API shape for future full implementation.
+/// </summary>
+public sealed class TestCluster : IDisposable
+{
+    private readonly string _name;
+    private readonly int _numServers;
+    private bool _disposed;
+
+    public string Name => _name;
+
+    private TestCluster(string name, int numServers)
+    {
+        _name = name;
+        _numServers = numServers;
+    }
+
+    /// <summary>
+    /// Creates a JetStream cluster with the given number of servers.
+    /// Throws <see cref="ClusterNotAvailableException"/> if no cluster is available.
+    /// </summary>
+    public static TestCluster CreateJetStreamCluster(int numServers, string name = "JSC")
+    {
+        throw new ClusterNotAvailableException(
+            $"No JetStream cluster available. Set NATS_INTEGRATION_TESTS=true and ensure {numServers}-node cluster '{name}' is running.");
+    }
+
+    /// <summary>
+    /// Creates a JetStream cluster with the specified configuration template.
+    /// </summary>
+    public static TestCluster CreateJetStreamClusterWithTemplate(string template, int numServers, string name = "JSC")
+    {
+        throw new ClusterNotAvailableException(
+            $"No JetStream cluster available for template cluster '{name}'.");
+    }
+
+    public void WaitOnClusterReady() { }
+    public void WaitOnLeader() { }
+    public void WaitOnStreamLeader(string account, string stream) { }
+    public void WaitOnConsumerLeader(string account, string stream, string consumer) { }
+    public void WaitOnPeerCount(int count) { }
+    public void WaitOnServerCurrent(object server) { }
+    public void WaitOnStreamCurrent(object server, string account, string stream) { }
+
+    public object Leader() => throw new ClusterNotAvailableException("Cluster not available.");
+    public object RandomServer() => throw new ClusterNotAvailableException("Cluster not available.");
+    public object RandomNonLeader() => throw new ClusterNotAvailableException("Cluster not available.");
+    public object RandomNonStreamLeader(string account, string stream) => throw new ClusterNotAvailableException("Cluster not available.");
+    public object ServerByName(string name) => throw new ClusterNotAvailableException("Cluster not available.");
+    public object StreamLeader(string account, string stream) => throw new ClusterNotAvailableException("Cluster not available.");
+    public object ConsumerLeader(string account, string stream, string consumer) => throw new ClusterNotAvailableException("Cluster not available.");
+
+    public void Dispose()
+    {
+        if (!_disposed)
+        {
+            _disposed = true;
+        }
+    }
+}
+
+/// <summary>
+/// Thrown when a test cluster is not available for integration testing.
+/// </summary>
+public sealed class ClusterNotAvailableException : Exception
+{
+    public ClusterNotAvailableException(string message) : base(message) { }
+}

dotnet/tests/ZB.MOM.NatsNet.Server.IntegrationTests/ZB.MOM.NatsNet.Server.IntegrationTests.csproj

@@ -17,13 +17,17 @@
     <PackageReference Include="Microsoft.NET.Test.Sdk" Version="17.14.1" />
     <PackageReference Include="NATS.Client.Core" Version="2.7.2" />
     <PackageReference Include="xunit" Version="2.9.3" />
+    <PackageReference Include="xunit.abstractions" Version="2.0.3" />
     <PackageReference Include="xunit.runner.visualstudio" Version="3.1.4" />
+    <PackageReference Include="Xunit.SkippableFact" Version="1.5.61" />
     <PackageReference Include="Shouldly" Version="*" />
     <PackageReference Include="NSubstitute" Version="*" />
   </ItemGroup>
 
   <ItemGroup>
     <Using Include="Xunit" />
+    <Using Include="Xunit.Abstractions" />
+    <Using Include="ZB.MOM.NatsNet.Server.IntegrationTests.Helpers" />
   </ItemGroup>
 
 </Project>