fix(time): preserve MCPError through call_tool handlers

Re-raise MCPError instead of wrapping it as ValueError, extract
create_tool_handlers for unit tests, and cover list/call paths.

Co-authored-by: Cursor <cursoragent@cursor.com>

Author: KarlLeen

src/time/src/mcp_server_time/server.py

@@ -128,7 +128,8 @@ def convert_time(
         )
 
 
-async def serve(local_timezone: str | None = None) -> None:
+def create_tool_handlers(local_timezone: str | None = None):
+    """Build list_tools / call_tool handlers for the time MCP server."""
     time_server = TimeServer()
     local_tz = str(get_local_tz(local_timezone))
 
@@ -224,9 +225,16 @@ async def call_tool(
                 ]
             )
 
+        except MCPError:
+            raise
         except Exception as e:
             raise ValueError(f"Error processing mcp-server-time query: {str(e)}")
 
+    return list_tools, call_tool
+
+
+async def serve(local_timezone: str | None = None) -> None:
+    list_tools, call_tool = create_tool_handlers(local_timezone)
     server = Server(
         "mcp-time",
         on_list_tools=list_tools,

src/time/test/time_server_test.py

@@ -1,11 +1,15 @@
 
+import asyncio
+import json
+
 from freezegun import freeze_time
 from mcp.shared.exceptions import MCPError
+from mcp.types import CallToolRequestParams, INVALID_PARAMS
 import pytest
 from unittest.mock import patch
 from zoneinfo import ZoneInfo
 
-from mcp_server_time.server import TimeServer, get_local_tz
+from mcp_server_time.server import TimeServer, create_tool_handlers, get_local_tz
 
 
 @pytest.mark.parametrize(
@@ -526,3 +530,59 @@ def test_get_local_tz_various_timezones(mock_get_localzone, timezone_name):
     result = get_local_tz()
     assert str(result) == timezone_name
     assert isinstance(result, ZoneInfo)
+
+
+def test_list_tools_returns_expected_tools():
+    list_tools, _ = create_tool_handlers("UTC")
+
+    async def _run():
+        return await list_tools(None, None)  # type: ignore[arg-type]
+
+    result = asyncio.run(_run())
+    assert [tool.name for tool in result.tools] == [
+        "get_current_time",
+        "convert_time",
+    ]
+
+
+def test_call_tool_get_current_time():
+    _, call_tool = create_tool_handlers("UTC")
+    params = CallToolRequestParams(
+        name="get_current_time",
+        arguments={"timezone": "Europe/Warsaw"},
+    )
+
+    async def _run():
+        with freeze_time("2024-01-01 12:00:00+00:00"):
+            return await call_tool(None, params)  # type: ignore[arg-type]
+
+    result = asyncio.run(_run())
+    payload = json.loads(result.content[0].text)
+    assert payload["timezone"] == "Europe/Warsaw"
+    assert payload["datetime"] == "2024-01-01T13:00:00+01:00"
+
+
+def test_call_tool_invalid_timezone_raises_mcp_error():
+    _, call_tool = create_tool_handlers("UTC")
+    params = CallToolRequestParams(
+        name="get_current_time",
+        arguments={"timezone": "Invalid/Timezone"},
+    )
+
+    async def _run():
+        await call_tool(None, params)  # type: ignore[arg-type]
+
+    with pytest.raises(MCPError) as exc_info:
+        asyncio.run(_run())
+    assert exc_info.value.code == INVALID_PARAMS
+
+
+def test_call_tool_unknown_tool_raises_value_error():
+    _, call_tool = create_tool_handlers("UTC")
+    params = CallToolRequestParams(name="unknown_tool", arguments={})
+
+    async def _run():
+        await call_tool(None, params)  # type: ignore[arg-type]
+
+    with pytest.raises(ValueError, match="Error processing mcp-server-time query"):
+        asyncio.run(_run())