Simulating the passing of time in unittesting

Question

I\'ve built a paywalled CMS + invoicing system for a client and I need to get more stringent with my testing.

I keep all my data in a Django ORM and have a bunch of Cele

Answer 1

You can use mock to change the return value of the function you use to get the time (datetime.datetime.now for example).

There are various ways to do so (see the mock documentation), but here is one :

import unittest
import datetime
from mock import patch

class SomeTestCase(unittest.TestCase):
    def setUp(self):
        self.time = datetime.datetime(2012, 5, 18)
        class fakedatetime(datetime.datetime):
            @classmethod
            def now(cls):
                return self.time
        patcher = patch('datetime.datetime', fakedatetime)
        self.addCleanup(patcher.stop)
        patcher.start()

    def test_something(self):
        self.assertEqual(datetime.datetime.now(), datetime.datetime(2012, 5, 18))
        self.time = datetime.datetime(2012, 5, 20)
        self.assertEqual(datetime.datetime.now(), datetime.datetime(2012, 5, 20))

Because we can't replace directly datetime.datetime.now, we create a fake datetime class that does everything the same way, except returning a constant value when now is called.