Add Python's socketserver.ThreadingMixin to the threaded test HTTP se…

…rver, and enable the 'daemon_threads' setting

Ref: https://docs.python.org/3/library/socketserver.html#socketserver.ThreadingMixIn

tests/utils.py

@@ -1,6 +1,7 @@
 import contextlib
 import http.server
 import pathlib
+import socketserver
 import threading
 from ssl import PROTOCOL_TLS_SERVER, SSLContext
 
@@ -16,10 +17,14 @@
 LOCK_PATH = str(TESTS_ROOT / 'test-server.lock')
 
 
+class ThreadedHttpServer(socketserver.ThreadingMixIn, http.server.HTTPServer):
+    daemon_threads = True
+
+
 class HttpServerThread(threading.Thread):
     def __init__(self, handler, *args, **kwargs):
         super().__init__(*args, **kwargs)
-        self.server = http.server.HTTPServer(("localhost", 7777), handler)
+        self.server = ThreadedHttpServer(("localhost", 7777), handler)
 
     def run(self):
         self.server.serve_forever(poll_interval=0.001)