Add tests for null collections behavior

Added NullCollectionTests class to verify that handlers are NOT synthesized
when collections are explicitly null. These tests ensure we don't unnecessarily
create capabilities when nothing is configured.

Co-authored-by: stephentoub <[email protected]>

Author: Copilot

tests/ModelContextProtocol.Tests/Server/EmptyCollectionTests.cs

@@ -158,3 +158,72 @@ public async Task EmptyPromptCollection_CanGetPromptAfterAddingDynamically()
         Assert.Equal("dynamic prompt content", ((TextContent)result.Messages[0].Content[0]).Text);
     }
 }
+
+/// <summary>
+/// Tests to verify that handlers are NOT synthesized when collections are null.
+/// This ensures we don't unnecessarily create capabilities when nothing is configured.
+/// </summary>
+public class NullCollectionTests : ClientServerTestBase
+{
+    public NullCollectionTests(ITestOutputHelper testOutputHelper)
+        : base(testOutputHelper)
+    {
+    }
+
+    protected override void ConfigureServices(ServiceCollection services, IMcpServerBuilder mcpServerBuilder)
+    {
+        mcpServerBuilder.Services.Configure<McpServerOptions>(options =>
+        {
+            options.ServerInfo = new Implementation
+            {
+                Name = "null-collection-test",
+                Version = "1.0.0"
+            };
+
+            // Explicitly leave collections as null - no handlers should be synthesized
+            options.ResourceCollection = null;
+            options.ToolCollection = null;
+            options.PromptCollection = null;
+        });
+    }
+
+    [Fact]
+    public void NullCollections_DoNotCreateCapabilities()
+    {
+        // Verify that when collections are null (and no handlers are provided),
+        // the specific capability properties remain null
+        Assert.Null(Server.ServerCapabilities.Resources);
+        Assert.Null(Server.ServerCapabilities.Tools);
+        Assert.Null(Server.ServerCapabilities.Prompts);
+    }
+
+    [Fact]
+    public async Task NullResourceCollection_ListReturnsEmpty()
+    {
+        using var client = await CreateMcpClientForServer();
+
+        // When no resource capability is configured, list should return empty
+        var resources = await client.ListResourcesAsync();
+        Assert.Empty(resources);
+    }
+
+    [Fact]
+    public async Task NullToolCollection_ListReturnsEmpty()
+    {
+        using var client = await CreateMcpClientForServer();
+
+        // When no tool capability is configured, list should return empty
+        var tools = await client.ListToolsAsync();
+        Assert.Empty(tools);
+    }
+
+    [Fact]
+    public async Task NullPromptCollection_ListReturnsEmpty()
+    {
+        using var client = await CreateMcpClientForServer();
+
+        // When no prompt capability is configured, list should return empty
+        var prompts = await client.ListPromptsAsync();
+        Assert.Empty(prompts);
+    }
+}