Merge #14333: fix test_queue so it can be run via standard unittest test discovery.

Lib/test/test_queue.py

@@ -82,7 +82,7 @@ class BlockingTestMixin:
                 self.fail("trigger thread ended but event never set")
 
 
-class BaseQueueTest(unittest.TestCase, BlockingTestMixin):
+class BaseQueueTestMixin(BlockingTestMixin):
     def setUp(self):
         self.cum = 0
         self.cumlock = threading.Lock()
@@ -229,13 +229,13 @@ class BaseQueueTest(unittest.TestCase, BlockingTestMixin):
         with self.assertRaises(queue.Full):
             q.put_nowait(4)
 
-class QueueTest(BaseQueueTest):
+class QueueTest(BaseQueueTestMixin, unittest.TestCase):
     type2test = queue.Queue
 
-class LifoQueueTest(BaseQueueTest):
+class LifoQueueTest(BaseQueueTestMixin, unittest.TestCase):
     type2test = queue.LifoQueue
 
-class PriorityQueueTest(BaseQueueTest):
+class PriorityQueueTest(BaseQueueTestMixin, unittest.TestCase):
     type2test = queue.PriorityQueue