Testing code that requires a Flask app or request context

I am getting working outside of request context when trying to access session in a test. How can I set up a context when I'm testing something that requires one?

import unittest
from flask import Flask, session

app = Flask(__name__)

@app.route('/')
def hello_world():
    t = Test()
    hello = t.hello()
    return hello

class Test:
    def hello(self):
        session['h'] = 'hello'
        return session['h']

class MyUnitTest(unittest.TestCase):
    def test_unit(self):
        t = tests.Test()
        t.hello()

If you want to make a request to your application, use the test_client.

c = app.test_client()
response = c.get('/test/url')
# test response

If you want to test code which uses an application context (current_app, g, url_for), push an app_context.

with app.app_context():
    # test your app context code

If you want test code which uses a request context (request, session), push a test_request_context.

with current_app.test_request_context():
    # test your request context code

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Both app and request contexts can also be pushed manually, which is useful when using the interpreter.

>>> ctx = app.app_context()
>>> ctx.push()

Flask-Script or the new Flask cli will automatically push an app context when running the shell command.

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Flask-Testing is a useful library that contains helpers for testing Flask apps.