Mocking python imports

__init__.py

#everyone loves a __init__ file

my_module.py

from third_party_module import World

class MyModule(object):
    """
    My shining class
    """

    def __init__(self):
        """
        Let's instanciate the World (muhaha)
        """

        self.world = World()

    def hello(self):
        """
        My shining method
        """

        self.world.say("hello")

test_bad_module.py

from unittest import TestCase
from mock import MagicMock

from my_module import MyModule

class TestBadMyModule(TestCase):
    """
    Let's test my module!
    """

    def test_hello_should_say_waitforit_hello(self):
        """
        We want to test that the hello method calls the say function with the string "hello:
        """

        m = MyModule()
        m.world = MagicMock()
        m.hello()

        m.world.say.assert_called_once_with("hello")

test_good_module.py

from unittest import TestCase
from mock import patch, MagicMock


class TestGoodMyModule(TestCase):
    """
    Let's test my module properly
    """

    def setUp(self):
        """
        It's patching time
        """

        #http://www.voidspace.org.uk/python/mock/examples.html#mocking-imports-with-patch-dict
        self.internetz_mock = MagicMock()
        self.internetz_mock.the.internetz.everything.log.return_value = True
        modules = {
            'the': self.internetz_mock,
            'the.internetz': self.internetz_mock.internetz,
        }

        self.module_patcher = patch.dict('sys.modules', modules)
        self.module_patcher.start()
        from my_module import MyModule
        self.my_module = MyModule

    def tearDown(self):
        """
        Let's clean up
        """

        self.module_patcher.stop()

    def test_hello_should_say_waitforit_hello(self):
        """
        We want to test that the hello method calls the say function with the string "hello:
        """

        m = self.my_module()
        m.world = MagicMock()
        m.hello()

        m.world.say.assert_called_once_with("hello")

third_party_module.py

from the.internetz import everything

class World(object):
    """
    what a grand class
    """

    def say(self, msg):
        """
        It speaks!
        """

        everything.log(msg)

        print msg