Use `pytest-jupyterhub` for testing

[Jeremy Tuloup]

There is now a Pytest plugin for JupyterHub: https://github.com/jupyterhub/pytest-jupyterhub

We should look into using it to simplify the current conftest:

tljh-repo2docker/tljh_repo2docker/tests/conftest.py

Lines 53 to 80 in c42f08a

 @pytest.fixture(scope='module') 
 def app(request, io_loop): 
     """ 
     Adapted from: 
     https://github.com/jupyterhub/jupyterhub/blob/8a3790b01ff944c453ffcc0486149e2a58ffabea/jupyterhub/tests/conftest.py#L74 
     """ 
  
     mocked_app = MockHub.instance() 
     c = DummyConfig() 
     c.JupyterHub = mocked_app 
     tljh_custom_jupyterhub_config(c) 
  
     async def make_app(): 
         await mocked_app.initialize([]) 
         await mocked_app.start() 
  
     def fin(): 
         # disconnect logging during cleanup because pytest closes captured FDs prematurely 
         mocked_app.log.handlers = [] 
         MockHub.clear_instance() 
         try: 
             mocked_app.stop() 
         except Exception as e: 
             print("Error stopping Hub: %s" % e, file=sys.stderr) 
  
     request.addfinalizer(fin) 
     io_loop.run_sync(make_app) 
     return mocked_app