Python: How do I mock datetime.utcnow()?

Question

I have the below:

from datetime import datetime

def get_report_month_key():
    month_for_report = datetime.utcnow()
    return month_for_report.strftime(\"         


        

Answer 1

The accepted answer by dasjotre works if you don't create any datetime instances in the module you are testing. If you try to create a datetime it will create a Mock object instead of one with the expected methods on a standard datetime object. This is because it replaces the whole class definition with a mock. Instead of doing this, you can use a similar approach to create the mocked definition by using datetime as the base.

mymodule.py

from datetime import datetime

def after_y2k():
    y2k = datetime(2000, 1, 1)
    return y2k < datetime.utcnow()

test_mymodule.py

import unittest
import datetime
from mock import patch, Mock
import mymodule
from mymodule import after_y2k


class ModuleTests(unittest.TestCase):
    @patch.object(mymodule, 'datetime', Mock(wraps=datetime.datetime))
    def test_after_y2k_passes(self):
        # Mock the return and run your test (Note you are doing it on your module)
        mymodule.datetime.utcnow.return_value = datetime.datetime(2002, 01, 01)
        self.assertEqual(True, after_y2k())

        mymodule.datetime.utcnow.return_value = datetime.datetime(1999, 01, 01)
        self.assertEqual(False, after_y2k())

    @patch('mymodule.datetime')
    def test_after_y2k_fails(self, mock_dt):
        # Run your tests
        mock_dt.utcnow = Mock(return_value=datetime.datetime(2002, 01, 01))
        self.assertEqual(True, after_y2k())

        # FAILS!!! because the object returned by utcnow is a MagicMock w/o 
        # datetime methods like "__lt__"
        mock_dt.utcnow = Mock(return_value=datetime.datetime(1999, 01, 01))
        self.assertEqual(False, after_y2k())