Add serialization roundtrip tests for all Protocol namespace types (#1289)

Co-authored-by: copilot-swe-agent[bot] <198982749+Copilot@users.noreply.github.com>
Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

tests/ModelContextProtocol.Tests/Protocol/McpTasksCapabilityTests.cs

@@ -0,0 +1,91 @@
+using ModelContextProtocol.Protocol;
+using System.Text.Json;
+
+namespace ModelContextProtocol.Tests.Protocol;
+
+public static class McpTasksCapabilityTests
+{
+    [Fact]
+    public static void McpTasksCapability_SerializationRoundTrip_WithAllProperties()
+    {
+        // Arrange
+        var original = new McpTasksCapability
+        {
+            List = new ListMcpTasksCapability(),
+            Cancel = new CancelMcpTasksCapability(),
+            Requests = new RequestMcpTasksCapability
+            {
+                Tools = new ToolsMcpTasksCapability
+                {
+                    Call = new CallToolMcpTasksCapability()
+                },
+                Sampling = new SamplingMcpTasksCapability
+                {
+                    CreateMessage = new CreateMessageMcpTasksCapability()
+                },
+                Elicitation = new ElicitationMcpTasksCapability
+                {
+                    Create = new CreateElicitationMcpTasksCapability()
+                }
+            }
+        };
+
+        // Act
+        string json = JsonSerializer.Serialize(original, McpJsonUtilities.DefaultOptions);
+        var deserialized = JsonSerializer.Deserialize<McpTasksCapability>(json, McpJsonUtilities.DefaultOptions);
+
+        // Assert
+        Assert.NotNull(deserialized);
+        Assert.NotNull(deserialized.List);
+        Assert.NotNull(deserialized.Cancel);
+        Assert.NotNull(deserialized.Requests);
+        Assert.NotNull(deserialized.Requests.Tools);
+        Assert.NotNull(deserialized.Requests.Tools.Call);
+        Assert.NotNull(deserialized.Requests.Sampling);
+        Assert.NotNull(deserialized.Requests.Sampling.CreateMessage);
+        Assert.NotNull(deserialized.Requests.Elicitation);
+        Assert.NotNull(deserialized.Requests.Elicitation.Create);
+    }
+
+    [Fact]
+    public static void McpTasksCapability_SerializationRoundTrip_WithMinimalProperties()
+    {
+        // Arrange
+        var original = new McpTasksCapability();
+
+        // Act
+        string json = JsonSerializer.Serialize(original, McpJsonUtilities.DefaultOptions);
+        var deserialized = JsonSerializer.Deserialize<McpTasksCapability>(json, McpJsonUtilities.DefaultOptions);
+
+        // Assert
+        Assert.NotNull(deserialized);
+        Assert.Null(deserialized.List);
+        Assert.Null(deserialized.Cancel);
+        Assert.Null(deserialized.Requests);
+    }
+
+    [Fact]
+    public static void McpTasksCapability_HasCorrectJsonPropertyNames()
+    {
+        var capability = new McpTasksCapability
+        {
+            List = new ListMcpTasksCapability(),
+            Cancel = new CancelMcpTasksCapability(),
+            Requests = new RequestMcpTasksCapability
+            {
+                Tools = new ToolsMcpTasksCapability
+                {
+                    Call = new CallToolMcpTasksCapability()
+                }
+            }
+        };
+
+        string json = JsonSerializer.Serialize(capability, McpJsonUtilities.DefaultOptions);
+
+        Assert.Contains("\"list\":", json);
+        Assert.Contains("\"cancel\":", json);
+        Assert.Contains("\"requests\":", json);
+        Assert.Contains("\"tools\":", json);
+        Assert.Contains("\"call\":", json);
+    }
+}