I can't get mock to work

Question

I'm trying to use a mock for unit testing with Python/Django but I just can't get it to work. The mock acts like it has never been called.

tests.py

from my_module import my_library
my_library = MagicMock()

class MyTest(TestCase):
    def test_add(self):
        acronym = 'TEST'

        m = MyModel(acronym=acronym)
        m.save()

        my_library.add.assert_called_with(acronym=acronym)

my_library.py

def add(acronym):
    # Processing...

models.py

class MyModel(Model):
    acronym = CharField(max_length=4)

    def save(self):
        my_library.add(acronym=self.acronym)

        super(MyModel, self).save(*args, **kwargs)

My library works, I know the function add is correctly called. But the mock doesn't seem to work because it just raises en exception when I run the unit tests:

AssertionError: Expected call: add(acronym='TEST')
Not called

I think I don't correctly use the mock thing. Can anyone help or give advice please?

Answer 1

That is because it is never called. The first line of your program does this:

my_library = __import__("my_module")

The next line just overshadows the first. It does not alter my_module in any way, thus all your other code just calls the original code instead of the mock.

Take a look at mock.patch instead. Either like this:

from mock import patch
import my_module as my_library

class MyTest(TestCase):
    def test_add(self):
        acronym = 'TEST'
        with patch.object(my_library, 'add') as add_method:   
            m = MyModel(acronym=acronym)
            m.save()
            add_method.assert_called_with(acronym=acronym)

Or using the original module name:

from mock import patch

class MyTest(TestCase):
    def test_add(self):
        acronym = 'TEST'
        with patch('my_module.add') as add_method:   
            m = MyModel(acronym=acronym)
            m.save()
            add_method.assert_called_with(acronym=acronym)