Remove 3.6 compatibility shims

- asyncio.all_tasks/current_task
- pytest-asyncio 0.17
- contextmanager.nullcontext

jupyterhub/tests/conftest.py

@@ -54,28 +54,6 @@ from .utils import add_user
 _db = None
 
 
-def _pytest_collection_modifyitems(items):
-    """This function is automatically run by pytest passing all collected test
-    functions.
-
-    We use it to add asyncio marker to all async tests and assert we don't use
-    test functions that are async generators which wouldn't make sense.
-
-    It is no longer required with pytest-asyncio >= 0.17
-    """
-    for item in items:
-        if inspect.iscoroutinefunction(item.obj):
-            item.add_marker('asyncio')
-        assert not inspect.isasyncgenfunction(item.obj)
-
-
-if sys.version_info < (3, 7):
-    # apply pytest-asyncio's 'auto' mode on Python 3.6.
-    # 'auto' mode is new in pytest-asyncio 0.17,
-    # which requires Python 3.7.
-    pytest_collection_modifyitems = _pytest_collection_modifyitems
-
-
 @fixture(scope='module')
 def ssl_tmpdir(tmpdir_factory):
     return tmpdir_factory.mktemp('ssl')