test native async generator on Python 3.6

jupyterhub/tests/test_api.py

@@ -798,15 +798,9 @@ def test_spawn_progress_bad(request, app, no_patience, bad_spawn):
     }
 
 
-@mark.gen_test
-def test_spawn_progress_cutoff(request, app, no_patience, slow_spawn):
-    """Progress events stop when Spawner finishes
-
-    even if progress iterator is still going.
-    """
-
-    @async_generator
-    async def progress_forever():
+@async_generator
+async def progress_forever():
+    """progress function that yields messages forever"""
     for i in range(1, 10):
         await yield_({
             'progress': i,
@@ -815,9 +809,36 @@ def test_spawn_progress_cutoff(request, app, no_patience, slow_spawn):
         # wait a long time before the next event
         await gen.sleep(10)
 
+
+if sys.version_info >= (3, 6):
+    # additional progress_forever defined as native
+    # async generator
+    # to test for issues with async_generator wrappers
+    exec("""
+async def progress_forever_native():
+    for i in range(1, 10):
+        yield {
+            'progress': i,
+            'message': 'Stage %s' % i,
+        }
+        # wait a long time before the next event
+        await gen.sleep(10)
+""", globals())
+
+
+@mark.gen_test
+def test_spawn_progress_cutoff(request, app, no_patience, slow_spawn):
+    """Progress events stop when Spawner finishes
+
+    even if progress iterator is still going.
+    """
     db = app.db
     name = 'geddy'
     app_user = add_user(db, app=app, name=name)
+    if sys.version_info >= (3, 6):
+        # Python >= 3.6, try native async generator
+        app_user.spawner.progress = globals()['progress_forever_native']
+    else:
         app_user.spawner.progress = progress_forever
     app_user.spawner.delay = 1