How do I know if my Flask application is ready to handle requests without actually polling?

During my smoke test, I want to make sure that the Flask app handles a few basic requests correctly. This involves starting your Flask application asynchronously:

class TestSmoke(unittest.TestCase):
    @staticmethod
    def run_server():
        app.run(port=49201)

    @classmethod
    def setUpClass(cls):
        cls.flaskProcess = multiprocessing.Process(target=TestSmoke.run_server)
        cls.flaskProcess.start()

      

        
        
        
      

    

and then run those tests that run queries against the library requests

.

If the code is left as is, tests are often executed before the server is started, resulting in ConnectionRefusedError

. To prevent this from happening, I added the following code to setUpClass

:

while True:
    try:
        requests.get("http://localhost:49201/", timeout=0.5)
        return
    except requests.exceptions.ConnectionError:
        pass

      

        
        
        
      

    

As long as it works, it looks ugly. Given that the test case is in control of the Flask application, there must be a way to notify it after the application is ready to handle requests. Unfortunately the closest thing I've found got_first_request

that doesn't help (unless I've polled the server already).

How can you tell if a Flask application is running and ready to handle requests when it starts up asynchronously?