Run tests in parallel

conftest.py

@@ -1,7 +1,9 @@
 # Copyright (c) Jupyter Development Team.
 # Distributed under the terms of the Modified BSD License.
+from contextlib import closing
 import os
 import logging
+import socket
 from typing import Any, Optional
 
 import docker
@@ -16,6 +18,14 @@ from requests.adapters import HTTPAdapter
 LOGGER = logging.getLogger(__name__)
 
 
+def find_free_port() -> str:
+    """Returns the available host port. Can be called in multiple threads/processes."""
+    with closing(socket.socket(socket.AF_INET, socket.SOCK_STREAM)) as s:
+        s.bind(("", 0))
+        s.setsockopt(socket.SOL_SOCKET, socket.SO_REUSEADDR, 1)
+        return s.getsockname()[1]
+
+
 @pytest.fixture(scope="session")
 def http_client() -> requests.Session:
     """Requests session with retries and backoff."""
@@ -108,14 +118,6 @@ class TrackedContainer:
         assert rv == 0 or rv["StatusCode"] == 0
         return logs
 
-    def get_host_port(self, container_port: str) -> str:
-        """Returns the host port associated with the tracked container's port."""
-        assert isinstance(self.container, Container)
-        self.container.reload()
-        return self.container.attrs["NetworkSettings"]["Ports"][container_port][0][
-            "HostPort"
-        ]
-
     @staticmethod
     def get_errors(logs: str) -> list[str]:
         return TrackedContainer._lines_starting_with(logs, "ERROR")