fix: Eliminate port allocation race condition in all affected test files

Extended the fix from test_integration.py to all test files that suffered
from the same TOCTOU (Time-of-Check-Time-of-Use) race condition. When
running with pytest-xdist parallel workers, multiple workers would get
the same "free" port from `socket.bind(("127.0.0.1", 0))`, leading to:
- "address already in use" errors
- Tests connecting to wrong servers

Solution:
- Updated 7 test files to use `get_worker_specific_port(worker_id)`:
  * tests/server/test_streamable_http_security.py
  * tests/server/test_sse_security.py
  * tests/shared/test_streamable_http.py (3 fixtures)
  * tests/shared/test_sse.py
  * tests/shared/test_ws.py
  * tests/client/test_http_unicode.py
  * tests/client/test_notification_response.py
- Fixed socket cleanup issue in tests/test_test_helpers.py

Each worker now gets an exclusive port range from 40000-59999, eliminating
the race condition across all test files that start servers.

Testing:
- All 703 tests pass with pytest-xdist parallel execution
- Port allocation now consistent across all parallel workers

Author: maxisbey

tests/client/test_http_unicode.py

@@ -14,6 +14,7 @@
 
 from mcp.client.session import ClientSession
 from mcp.client.streamable_http import streamablehttp_client
+from tests.test_helpers import get_worker_specific_port
 
 # Test constants with various Unicode characters
 UNICODE_TEST_STRINGS = {
@@ -145,11 +146,9 @@ async def lifespan(app: Starlette) -> AsyncGenerator[None, None]:
 
 
 @pytest.fixture
-def unicode_server_port() -> int:
+def unicode_server_port(worker_id: str) -> int:
     """Find an available port for the Unicode test server."""
-    with socket.socket() as s:
-        s.bind(("127.0.0.1", 0))
-        return s.getsockname()[1]
+    return get_worker_specific_port(worker_id)
 
 
 @pytest.fixture

tests/client/test_notification_response.py

@@ -22,6 +22,7 @@
 from mcp.client.streamable_http import streamablehttp_client
 from mcp.shared.session import RequestResponder
 from mcp.types import ClientNotification, RootsListChangedNotification
+from tests.test_helpers import get_worker_specific_port
 
 
 def create_non_sdk_server_app() -> Starlette:
@@ -81,11 +82,9 @@ def run_non_sdk_server(port: int) -> None:
 
 
 @pytest.fixture
-def non_sdk_server_port() -> int:
+def non_sdk_server_port(worker_id: str) -> int:
     """Get an available port for the test server."""
-    with socket.socket() as s:
-        s.bind(("127.0.0.1", 0))
-        return s.getsockname()[1]
+    return get_worker_specific_port(worker_id)
 
 
 @pytest.fixture

tests/server/test_sse_security.py

@@ -2,7 +2,6 @@
 
 import logging
 import multiprocessing
-import socket
 
 import httpx
 import pytest
@@ -16,17 +15,15 @@
 from mcp.server.sse import SseServerTransport
 from mcp.server.transport_security import TransportSecuritySettings
 from mcp.types import Tool
-from tests.test_helpers import wait_for_server
+from tests.test_helpers import get_worker_specific_port, wait_for_server
 
 logger = logging.getLogger(__name__)
 SERVER_NAME = "test_sse_security_server"
 
 
 @pytest.fixture
-def server_port() -> int:
-    with socket.socket() as s:
-        s.bind(("127.0.0.1", 0))
-        return s.getsockname()[1]
+def server_port(worker_id: str) -> int:
+    return get_worker_specific_port(worker_id)
 
 
 @pytest.fixture

tests/server/test_streamable_http_security.py

@@ -2,7 +2,6 @@
 
 import logging
 import multiprocessing
-import socket
 from collections.abc import AsyncGenerator
 from contextlib import asynccontextmanager
 
@@ -17,17 +16,15 @@
 from mcp.server.streamable_http_manager import StreamableHTTPSessionManager
 from mcp.server.transport_security import TransportSecuritySettings
 from mcp.types import Tool
-from tests.test_helpers import wait_for_server
+from tests.test_helpers import get_worker_specific_port, wait_for_server
 
 logger = logging.getLogger(__name__)
 SERVER_NAME = "test_streamable_http_security_server"
 
 
 @pytest.fixture
-def server_port() -> int:
-    with socket.socket() as s:
-        s.bind(("127.0.0.1", 0))
-        return s.getsockname()[1]
+def server_port(worker_id: str) -> int:
+    return get_worker_specific_port(worker_id)
 
 
 @pytest.fixture

tests/shared/test_sse.py

@@ -32,16 +32,14 @@
     TextResourceContents,
     Tool,
 )
-from tests.test_helpers import wait_for_server
+from tests.test_helpers import get_worker_specific_port, wait_for_server
 
 SERVER_NAME = "test_server_for_SSE"
 
 
 @pytest.fixture
-def server_port() -> int:
-    with socket.socket() as s:
-        s.bind(("127.0.0.1", 0))
-        return s.getsockname()[1]
+def server_port(worker_id: str) -> int:
+    return get_worker_specific_port(worker_id)
 
 
 @pytest.fixture

tests/shared/test_streamable_http.py

@@ -6,7 +6,6 @@
 
 import json
 import multiprocessing
-import socket
 from collections.abc import Generator
 from typing import Any
 
@@ -42,7 +41,7 @@
 from mcp.shared.message import ClientMessageMetadata
 from mcp.shared.session import RequestResponder
 from mcp.types import InitializeResult, TextContent, TextResourceContents, Tool
-from tests.test_helpers import wait_for_server
+from tests.test_helpers import get_worker_specific_port, wait_for_server
 
 # Test constants
 SERVER_NAME = "test_streamable_http_server"
@@ -322,19 +321,15 @@ def run_server(port: int, is_json_response_enabled: bool = False, event_store: E
 
 # Test fixtures - using same approach as SSE tests
 @pytest.fixture
-def basic_server_port() -> int:
+def basic_server_port(worker_id: str) -> int:
     """Find an available port for the basic server."""
-    with socket.socket() as s:
-        s.bind(("127.0.0.1", 0))
-        return s.getsockname()[1]
+    return get_worker_specific_port(worker_id)
 
 
 @pytest.fixture
-def json_server_port() -> int:
+def json_server_port(worker_id: str) -> int:
     """Find an available port for the JSON response server."""
-    with socket.socket() as s:
-        s.bind(("127.0.0.1", 0))
-        return s.getsockname()[1]
+    return get_worker_specific_port(worker_id)
 
 
 @pytest.fixture
@@ -360,11 +355,9 @@ def event_store() -> SimpleEventStore:
 
 
 @pytest.fixture
-def event_server_port() -> int:
+def event_server_port(worker_id: str) -> int:
     """Find an available port for the event store server."""
-    with socket.socket() as s:
-        s.bind(("127.0.0.1", 0))
-        return s.getsockname()[1]
+    return get_worker_specific_port(worker_id)
 
 
 @pytest.fixture

tests/shared/test_ws.py

@@ -1,5 +1,4 @@
 import multiprocessing
-import socket
 import time
 from collections.abc import AsyncGenerator, Generator
 from typing import Any
@@ -26,16 +25,14 @@
     TextResourceContents,
     Tool,
 )
-from tests.test_helpers import wait_for_server
+from tests.test_helpers import get_worker_specific_port, wait_for_server
 
 SERVER_NAME = "test_server_for_WS"
 
 
 @pytest.fixture
-def server_port() -> int:
-    with socket.socket() as s:
-        s.bind(("127.0.0.1", 0))
-        return s.getsockname()[1]
+def server_port(worker_id: str) -> int:
+    return get_worker_specific_port(worker_id)
 
 
 @pytest.fixture

tests/test_test_helpers.py

@@ -206,13 +206,20 @@ def test_get_worker_specific_port_raises_when_no_ports_available(monkeypatch: py
     try:
         # Try to bind all ports in range (may not succeed on all platforms)
         for port in range(start, min(start + 10, end)):  # Just bind first 10 for speed
+            s: socket.socket | None = None
             try:
                 s = socket.socket()
-                s.bind(("127.0.0.1", port))
-                sockets.append(s)
-            except OSError:
-                # Port already in use, skip
-                pass
+                try:
+                    s.bind(("127.0.0.1", port))
+                    sockets.append(s)
+                except OSError:
+                    # Port already in use, skip
+                    s.close()
+            except Exception:
+                # Clean up socket if any unexpected error
+                if s is not None:
+                    s.close()
+                raise
 
         # If we managed to bind some ports, temporarily exhaust the small range
         if sockets:
@@ -221,5 +228,5 @@ def test_get_worker_specific_port_raises_when_no_ports_available(monkeypatch: py
             pass
     finally:
         # Clean up sockets
-        for s in sockets:
-            s.close()
+        for sock in sockets:
+            sock.close()