Fix flaky port selection in registry tests

Depends on https://github.com/jarus/flask-testing/pull/98

[Fixes #136705135]

test/registry_tests.py

@@ -42,7 +42,6 @@ from image.docker.schema1 import DockerSchema1ManifestBuilder
 from initdb import wipe_database, initialize_database, populate_database
 from jsonschema import validate as validate_schema
 from util.security.registry_jwt import decode_bearer_header
-from test.testutil import get_open_port
 
 
 try:
@@ -240,7 +239,7 @@ class RegistryTestCaseMixin(LiveServerTestCase):
       app.config['DEBUG'] = True
 
     app.config['TESTING'] = True
-    app.config['LIVESERVER_PORT'] = get_open_port()
+    app.config['LIVESERVER_PORT'] = 0 # LiveServerTestCase will choose the port for us.
     app.config['DB_URI'] = get_new_database_uri()
     return app
 

test/testutil.py

@@ -1,14 +0,0 @@
-import socket
-
-def get_open_port():
-  """ Retrieves an open port on the system. """
-
-  # Bind a socket to a random port. We can then ask for the port number,
-  # and return it.
-  s = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
-  s.bind(("", 0))
-  s.listen(1)
-  port = s.getsockname()[1]
-  s.close()
-
-  return port