test: remove vanilla Pydantic serialization test

The test was originally validating the custom model_serializer on
JSONRPCError. With the model_serializer removed in favor of
exclude_unset, this test only exercises standard Pydantic behavior.
The null-id functionality is covered by E2E tests in test_session.py.

Author: maxisbey

tests/test_types.py

@@ -1,20 +1,16 @@
-import json
 from typing import Any
 
 import pytest
 
 from mcp.types import (
     LATEST_PROTOCOL_VERSION,
-    PARSE_ERROR,
     ClientCapabilities,
     CreateMessageRequestParams,
     CreateMessageResult,
     CreateMessageResultWithTools,
-    ErrorData,
     Implementation,
     InitializeRequest,
     InitializeRequestParams,
-    JSONRPCError,
     JSONRPCRequest,
     ListToolsResult,
     SamplingCapability,
@@ -364,20 +360,3 @@ def test_list_tools_result_preserves_json_schema_2020_12_fields():
     assert tool.input_schema["$schema"] == "https://json-schema.org/draft/2020-12/schema"
     assert "$defs" in tool.input_schema
     assert tool.input_schema["additionalProperties"] is False
-
-
-def test_jsonrpc_error_null_id_serialization_preserves_id():
-    """Test that id: null is preserved in JSON output with exclude_unset=True.
-
-    JSON-RPC 2.0 requires the id field to be present with value null for
-    parse errors, not absent entirely.
-    """
-    error = JSONRPCError(jsonrpc="2.0", id=None, error=ErrorData(code=PARSE_ERROR, message="Parse error"))
-    serialized = error.model_dump(by_alias=True, exclude_unset=True)
-    assert "id" in serialized
-    assert serialized["id"] is None
-
-    json_str = error.model_dump_json(by_alias=True, exclude_unset=True)
-    parsed = json.loads(json_str)
-    assert "id" in parsed
-    assert parsed["id"] is None