apply asyncio patch before launching new loop for tests

notebook/tests/launchnotebook.py

@@ -140,9 +140,6 @@ class NotebookTestBase(TestCase):
 
         started = Event()
         def start_thread():
-            if 'asyncio' in sys.modules:
-                import asyncio
-                asyncio.set_event_loop(asyncio.new_event_loop())
             app = cls.notebook = NotebookApp(
                 port=cls.port,
                 port_retries=0,
@@ -156,6 +153,10 @@ class NotebookTestBase(TestCase):
                 allow_root=True,
                 token=cls.token,
             )
+            if 'asyncio' in sys.modules:
+                app._init_asyncio_patch()
+                import asyncio
+                asyncio.set_event_loop(asyncio.new_event_loop())
             # don't register signal handler during tests
             app.init_signal = lambda : None
             # clear log handlers and propagate to root for nose to capture it