tests: implement readiness check before yielding local-http(s) test servers

CHANGES.rst

@@ -90,6 +90,9 @@ Bugs fixed
  Patch by Bénédikt Tran.
 * #12008: Fix case-sensitive lookup of ``std:label`` names in intersphinx inventory.
  Patch by Michael Goerz.
+* #12038: Resolve ``linkcheck`` unit test timeouts on Windows by adding a readiness
+ check to the test HTTP(S) server setup code.
+ Patch by James Addison.
 
 Testing
 -------

tests/utils.py

@@ -1,6 +1,7 @@
 import contextlib
 import http.server
 import pathlib
+import socket
 import threading
 from ssl import PROTOCOL_TLS_SERVER, SSLContext
 
@@ -15,11 +16,15 @@
 # File lock for tests
 LOCK_PATH = str(TESTS_ROOT / 'test-server.lock')
 
+HOST_NAME = "localhost"
+HOST_PORT = 7777
+ADDRESS = (HOST_NAME, HOST_PORT)
+
 
 class HttpServerThread(threading.Thread):
  def __init__(self, handler, *args, **kwargs):
  super().__init__(*args, **kwargs)
- self.server = http.server.ThreadingHTTPServer(("localhost", 7777), handler)
+ self.server = http.server.ThreadingHTTPServer(ADDRESS, handler)
 
  def run(self):
  self.server.serve_forever(poll_interval=0.001)
@@ -45,7 +50,8 @@ def server(handler):
  server_thread = thread_class(handler, daemon=True)
  server_thread.start()
  try:
- yield server_thread
+ socket.create_connection(ADDRESS, timeout=0.5).close() # Attempt connection.
+ yield server_thread # Connection has been confirmed possible; proceed.
  finally:
  server_thread.terminate()
  return contextlib.contextmanager(server)