Refactor self.event_queues in tests

Replace `self.event_queues` with property merging all event queues
from all schedulers and `self.additional_event_queues`.

This change intends to prepare tests for multi scheduler use.
It does not change anything outside the tests.

Change-Id: Ie1964d43db3fb064220cd7f3245f531490a6a025
Story: 2007192

tests/base.py

@@ -30,7 +30,8 @@ import queue
 import random
 import re
 from logging import Logger
-from typing import Callable, Optional, Any, Iterable
+from queue import Queue
+from typing import Callable, Optional, Any, Iterable, Generator, List
 
 import requests
 import select
@@ -3691,7 +3692,7 @@ class ZuulTestCase(BaseTestCase):
         gerritsource.GerritSource.replication_retry_interval = 0.5
         gerritconnection.GerritEventConnector.delay = 0.0
 
-        self.event_queues = []
+        self.additional_event_queues = []
         self.poller_events = {}
         self.configure_connections()
 
@@ -3707,12 +3708,11 @@ class ZuulTestCase(BaseTestCase):
         self.builds = self.executor_server.running_builds
 
         self.scheds = SchedulerTestManager()
-        sched_app = self.scheds.create(
+        self.scheds.create(
             self.log, self.config, self.zk_config, self.connections)
-        self.event_queues = sched_app.event_queues + self.event_queues
 
         if hasattr(self, 'fake_github'):
-            self.event_queues.append(
+            self.additional_event_queues.append(
                 self.fake_github.github_event_connector._event_forward_queue)
 
         self.merge_server = None
@@ -3722,6 +3722,12 @@ class ZuulTestCase(BaseTestCase):
         self.addCleanup(self.shutdown)
         self.addCleanup(self.assertFinalState)
 
+    def __event_queues(self, matcher) -> List[Queue]:
+        sched_queues = map(lambda app: app.event_queues,
+                           self.scheds.filter(matcher))
+        return [item for sublist in sched_queues for item in sublist] + \
+            self.additional_event_queues
+
     def configure_connections(self, source_only=False):
         # Set up gerrit related fakes
         # Set a changes database so multiple FakeGerrit's can report back to
@@ -3744,7 +3750,7 @@ class ZuulTestCase(BaseTestCase):
             if con.web_server:
                 self.addCleanup(con.web_server.stop)
 
-            self.event_queues.append(con.event_queue)
+            self.additional_event_queues.append(con.event_queue)
             setattr(self, 'fake_' + name, con)
             return con
 
@@ -3783,7 +3789,7 @@ class ZuulTestCase(BaseTestCase):
                 changes_db=db,
                 upstream_root=self.upstream_root,
                 git_url_with_auth=self.git_url_with_auth)
-            self.event_queues.append(con.event_queue)
+            self.additional_event_queues.append(con.event_queue)
             setattr(self, 'fake_' + name, con)
             registerGithubProjects(con)
             return con
@@ -3800,7 +3806,7 @@ class ZuulTestCase(BaseTestCase):
                 self.rpcclient,
                 changes_db=db,
                 upstream_root=self.upstream_root)
-            self.event_queues.append(con.event_queue)
+            self.additional_event_queues.append(con.event_queue)
             setattr(self, 'fake_' + name, con)
             return con
 
@@ -3816,7 +3822,7 @@ class ZuulTestCase(BaseTestCase):
                 self.rpcclient,
                 changes_db=db,
                 upstream_root=self.upstream_root)
-            self.event_queues.append(con.event_queue)
+            self.additional_event_queues.append(con.event_queue)
             setattr(self, 'fake_' + name, con)
             return con
 
@@ -4351,12 +4357,16 @@ class ZuulTestCase(BaseTestCase):
                 return False
         return True
 
-    def eventQueuesEmpty(self):
-        for event_queue in self.event_queues:
+    def __eventQueuesEmpty(self, matcher)\
+            -> Generator[bool, None, None]:
+        for event_queue in self.__event_queues(matcher):
             yield event_queue.empty()
 
-    def eventQueuesJoin(self):
-        for event_queue in self.event_queues:
+    def __eventQueuesJoin(self, matcher) -> None:
+        for app in self.scheds.filter(matcher):
+            for event_queue in app.event_queues:
+                event_queue.join()
+        for event_queue in self.additional_event_queues:
             event_queue.join()
 
     def waitUntilSettled(self, msg="", matcher=None) -> None:
@@ -4366,7 +4376,7 @@ class ZuulTestCase(BaseTestCase):
             if time.time() - start > self.wait_timeout:
                 self.log.error("Timeout waiting for Zuul to settle")
                 self.log.error("Queue status:")
-                for event_queue in self.event_queues:
+                for event_queue in self.__event_queues(matcher):
                     self.log.error("  %s: %s" %
                                    (event_queue, event_queue.empty()))
                 self.log.error("All builds waiting: %s" %
@@ -4386,14 +4396,14 @@ class ZuulTestCase(BaseTestCase):
             if self.__haveAllBuildsReported(matcher):
                 # Join ensures that the queue is empty _and_ events have been
                 # processed
-                self.eventQueuesJoin()
+                self.__eventQueuesJoin(matcher)
                 self.scheds.execute(
                     lambda app: app.sched.run_handler_lock.acquire())
                 if (self.__areAllMergeJobsWaiting(matcher) and
                     self.__haveAllBuildsReported(matcher) and
                     self.__areAllBuildsWaiting(matcher) and
                     self.__areAllNodeRequestsComplete(matcher) and
-                    all(self.eventQueuesEmpty())):
+                    all(self.__eventQueuesEmpty(matcher))):
                     # The queue empty check is placed at the end to
                     # ensure that if a component adds an event between
                     # when locked the run handler and checked that the