Add comprehensive tests for JsonRpcMessage.Converter optimization

- Test all message types: Request, Notification, Response, Error
- Test with various ID types (string, number)
- Test null result handling
- Test error handling for invalid messages
- Test round-trip serialization/deserialization
- Test unknown property handling
- All 16 new tests pass

Co-authored-by: eiriktsarpalis <2813363+eiriktsarpalis@users.noreply.github.com>

Author: Copilot

tests/ModelContextProtocol.Tests/Protocol/JsonRpcMessageConverterTests.cs

@@ -0,0 +1,305 @@
+using ModelContextProtocol.Protocol;
+using System.Text.Json;
+using System.Text.Json.Nodes;
+
+namespace ModelContextProtocol.Tests.Protocol;
+
+/// <summary>
+/// Tests for the optimized JsonRpcMessage.Converter implementation.
+/// </summary>
+public static class JsonRpcMessageConverterTests
+{
+    [Fact]
+    public static void Deserialize_JsonRpcRequest_WithAllProperties()
+    {
+        // Arrange
+        string json = """{"jsonrpc":"2.0","id":123,"method":"test/method","params":{"key":"value"}}""";
+
+        // Act
+        var message = JsonSerializer.Deserialize<JsonRpcMessage>(json, McpJsonUtilities.DefaultOptions);
+
+        // Assert
+        Assert.NotNull(message);
+        Assert.IsType<JsonRpcRequest>(message);
+        var request = (JsonRpcRequest)message;
+        Assert.Equal("2.0", request.JsonRpc);
+        Assert.Equal(new RequestId(123), request.Id);
+        Assert.Equal("test/method", request.Method);
+        Assert.NotNull(request.Params);
+        Assert.Equal("value", request.Params["key"]?.GetValue<string>());
+    }
+
+    [Fact]
+    public static void Deserialize_JsonRpcRequest_WithStringId()
+    {
+        // Arrange
+        string json = """{"jsonrpc":"2.0","id":"abc-123","method":"test/method"}""";
+
+        // Act
+        var message = JsonSerializer.Deserialize<JsonRpcMessage>(json, McpJsonUtilities.DefaultOptions);
+
+        // Assert
+        Assert.NotNull(message);
+        Assert.IsType<JsonRpcRequest>(message);
+        var request = (JsonRpcRequest)message;
+        Assert.Equal("2.0", request.JsonRpc);
+        Assert.Equal(new RequestId("abc-123"), request.Id);
+        Assert.Equal("test/method", request.Method);
+    }
+
+    [Fact]
+    public static void Deserialize_JsonRpcNotification_WithParams()
+    {
+        // Arrange
+        string json = """{"jsonrpc":"2.0","method":"notifications/progress","params":{"progress":50}}""";
+
+        // Act
+        var message = JsonSerializer.Deserialize<JsonRpcMessage>(json, McpJsonUtilities.DefaultOptions);
+
+        // Assert
+        Assert.NotNull(message);
+        Assert.IsType<JsonRpcNotification>(message);
+        var notification = (JsonRpcNotification)message;
+        Assert.Equal("2.0", notification.JsonRpc);
+        Assert.Equal("notifications/progress", notification.Method);
+        Assert.NotNull(notification.Params);
+        Assert.Equal(50, notification.Params["progress"]?.GetValue<int>());
+    }
+
+    [Fact]
+    public static void Deserialize_JsonRpcResponse_WithResult()
+    {
+        // Arrange
+        string json = """{"jsonrpc":"2.0","id":42,"result":{"status":"success","data":[1,2,3]}}""";
+
+        // Act
+        var message = JsonSerializer.Deserialize<JsonRpcMessage>(json, McpJsonUtilities.DefaultOptions);
+
+        // Assert
+        Assert.NotNull(message);
+        Assert.IsType<JsonRpcResponse>(message);
+        var response = (JsonRpcResponse)message;
+        Assert.Equal("2.0", response.JsonRpc);
+        Assert.Equal(new RequestId(42), response.Id);
+        Assert.NotNull(response.Result);
+        Assert.Equal("success", response.Result["status"]?.GetValue<string>());
+    }
+
+    [Fact]
+    public static void Deserialize_JsonRpcResponse_WithNullResult()
+    {
+        // Arrange
+        string json = """{"jsonrpc":"2.0","id":1,"result":null}""";
+
+        // Act
+        var message = JsonSerializer.Deserialize<JsonRpcMessage>(json, McpJsonUtilities.DefaultOptions);
+
+        // Assert
+        Assert.NotNull(message);
+        Assert.IsType<JsonRpcResponse>(message);
+        var response = (JsonRpcResponse)message;
+        Assert.Equal("2.0", response.JsonRpc);
+        Assert.Equal(new RequestId(1), response.Id);
+        Assert.Null(response.Result);
+    }
+
+    [Fact]
+    public static void Deserialize_JsonRpcError_WithErrorDetails()
+    {
+        // Arrange
+        string json = """{"jsonrpc":"2.0","id":"req-1","error":{"code":-32600,"message":"Invalid Request","data":"Additional error info"}}""";
+
+        // Act
+        var message = JsonSerializer.Deserialize<JsonRpcMessage>(json, McpJsonUtilities.DefaultOptions);
+
+        // Assert
+        Assert.NotNull(message);
+        Assert.IsType<JsonRpcError>(message);
+        var error = (JsonRpcError)message;
+        Assert.Equal("2.0", error.JsonRpc);
+        Assert.Equal(new RequestId("req-1"), error.Id);
+        Assert.NotNull(error.Error);
+        Assert.Equal(-32600, error.Error.Code);
+        Assert.Equal("Invalid Request", error.Error.Message);
+        Assert.Equal("Additional error info", error.Error.Data?.ToString());
+    }
+
+    [Fact]
+    public static void Deserialize_JsonRpcMessage_IgnoresUnknownProperties()
+    {
+        // Arrange - JSON with unknown properties
+        string json = """{"jsonrpc":"2.0","id":1,"method":"test","params":{},"extra":"ignored","another":123}""";
+
+        // Act
+        var message = JsonSerializer.Deserialize<JsonRpcMessage>(json, McpJsonUtilities.DefaultOptions);
+
+        // Assert - should successfully deserialize, ignoring unknown properties
+        Assert.NotNull(message);
+        Assert.IsType<JsonRpcRequest>(message);
+        var request = (JsonRpcRequest)message;
+        Assert.Equal("test", request.Method);
+    }
+
+    [Fact]
+    public static void Deserialize_InvalidJsonRpcVersion_ThrowsException()
+    {
+        // Arrange
+        string json = """{"jsonrpc":"1.0","id":1,"method":"test"}""";
+
+        // Act & Assert
+        var exception = Assert.Throws<JsonException>(() =>
+            JsonSerializer.Deserialize<JsonRpcMessage>(json, McpJsonUtilities.DefaultOptions));
+        Assert.Contains("jsonrpc version", exception.Message);
+    }
+
+    [Fact]
+    public static void Deserialize_MissingJsonRpcVersion_ThrowsException()
+    {
+        // Arrange
+        string json = """{"id":1,"method":"test"}""";
+
+        // Act & Assert
+        var exception = Assert.Throws<JsonException>(() =>
+            JsonSerializer.Deserialize<JsonRpcMessage>(json, McpJsonUtilities.DefaultOptions));
+        Assert.Contains("jsonrpc version", exception.Message);
+    }
+
+    [Fact]
+    public static void Deserialize_ResponseWithoutResultOrError_ThrowsException()
+    {
+        // Arrange
+        string json = """{"jsonrpc":"2.0","id":1}""";
+
+        // Act & Assert
+        var exception = Assert.Throws<JsonException>(() =>
+            JsonSerializer.Deserialize<JsonRpcMessage>(json, McpJsonUtilities.DefaultOptions));
+        Assert.Contains("result or error", exception.Message);
+    }
+
+    [Fact]
+    public static void Deserialize_InvalidMessageFormat_ThrowsException()
+    {
+        // Arrange - neither request nor response nor notification
+        string json = """{"jsonrpc":"2.0"}""";
+
+        // Act & Assert
+        var exception = Assert.Throws<JsonException>(() =>
+            JsonSerializer.Deserialize<JsonRpcMessage>(json, McpJsonUtilities.DefaultOptions));
+        Assert.Contains("Invalid JSON-RPC message format", exception.Message);
+    }
+
+    [Fact]
+    public static void Serialize_JsonRpcRequest_ProducesCorrectJson()
+    {
+        // Arrange
+        var request = new JsonRpcRequest
+        {
+            JsonRpc = "2.0",
+            Id = new RequestId(123),
+            Method = "test/method",
+            Params = JsonNode.Parse("""{"key":"value"}""")
+        };
+
+        // Act
+        string json = JsonSerializer.Serialize<JsonRpcMessage>(request, McpJsonUtilities.DefaultOptions);
+
+        // Assert
+        Assert.Contains("\"jsonrpc\":\"2.0\"", json);
+        Assert.Contains("\"id\":123", json);
+        Assert.Contains("\"method\":\"test/method\"", json);
+        Assert.Contains("\"key\":\"value\"", json);
+    }
+
+    [Fact]
+    public static void Serialize_JsonRpcNotification_ProducesCorrectJson()
+    {
+        // Arrange
+        var notification = new JsonRpcNotification
+        {
+            JsonRpc = "2.0",
+            Method = "notifications/test"
+        };
+
+        // Act
+        string json = JsonSerializer.Serialize<JsonRpcMessage>(notification, McpJsonUtilities.DefaultOptions);
+
+        // Assert
+        Assert.Contains("\"jsonrpc\":\"2.0\"", json);
+        Assert.Contains("\"method\":\"notifications/test\"", json);
+        Assert.DoesNotContain("\"id\"", json);
+    }
+
+    [Fact]
+    public static void RoundTrip_Request_PreservesData()
+    {
+        // Arrange
+        var original = new JsonRpcRequest
+        {
+            JsonRpc = "2.0",
+            Id = new RequestId("test-id"),
+            Method = "some/method",
+            Params = JsonNode.Parse("""{"nested":{"value":42}}""")
+        };
+
+        // Act
+        string json = JsonSerializer.Serialize<JsonRpcMessage>(original, McpJsonUtilities.DefaultOptions);
+        var deserialized = JsonSerializer.Deserialize<JsonRpcMessage>(json, McpJsonUtilities.DefaultOptions) as JsonRpcRequest;
+
+        // Assert
+        Assert.NotNull(deserialized);
+        Assert.Equal(original.JsonRpc, deserialized.JsonRpc);
+        Assert.Equal(original.Id, deserialized.Id);
+        Assert.Equal(original.Method, deserialized.Method);
+        Assert.Equal(42, deserialized.Params?["nested"]?["value"]?.GetValue<int>());
+    }
+
+    [Fact]
+    public static void RoundTrip_Response_PreservesData()
+    {
+        // Arrange
+        var original = new JsonRpcResponse
+        {
+            JsonRpc = "2.0",
+            Id = new RequestId(999),
+            Result = JsonNode.Parse("""{"success":true,"items":[1,2,3]}""")
+        };
+
+        // Act
+        string json = JsonSerializer.Serialize<JsonRpcMessage>(original, McpJsonUtilities.DefaultOptions);
+        var deserialized = JsonSerializer.Deserialize<JsonRpcMessage>(json, McpJsonUtilities.DefaultOptions) as JsonRpcResponse;
+
+        // Assert
+        Assert.NotNull(deserialized);
+        Assert.Equal(original.JsonRpc, deserialized.JsonRpc);
+        Assert.Equal(original.Id, deserialized.Id);
+        Assert.True(deserialized.Result?["success"]?.GetValue<bool>());
+    }
+
+    [Fact]
+    public static void RoundTrip_Error_PreservesData()
+    {
+        // Arrange
+        var original = new JsonRpcError
+        {
+            JsonRpc = "2.0",
+            Id = new RequestId(100),
+            Error = new JsonRpcErrorDetail
+            {
+                Code = -32601,
+                Message = "Method not found",
+                Data = "test/unknown"
+            }
+        };
+
+        // Act
+        string json = JsonSerializer.Serialize<JsonRpcMessage>(original, McpJsonUtilities.DefaultOptions);
+        var deserialized = JsonSerializer.Deserialize<JsonRpcMessage>(json, McpJsonUtilities.DefaultOptions) as JsonRpcError;
+
+        // Assert
+        Assert.NotNull(deserialized);
+        Assert.Equal(original.JsonRpc, deserialized.JsonRpc);
+        Assert.Equal(original.Id, deserialized.Id);
+        Assert.Equal(original.Error.Code, deserialized.Error.Code);
+        Assert.Equal(original.Error.Message, deserialized.Error.Message);
+    }
+}