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()

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

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

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

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