Django tests - patch object in all tests

Question

I need to create some kind of MockMixin for my tests. It should include mocks for everything that calls external sources. For example, each time I save model in

Answer 1

I ended up creating a test runner to serve my purpose. I needed to mock the file storage so that images do not actually write to the file system while testing. The images object is being called in many tests thus patching each class would not be DRY. Also, I noticed that mocking the file itself would leave it on the system in case the test failed. But this method didn't.

I created a file runner.py in the project root

# runner.py
from unittest.mock import patch

from django.test.runner import DiscoverRunner

from myapp.factories import ImageFactory


class UnitTestRunner(DiscoverRunner):

    @patch('django.core.files.storage.FileSystemStorage.save')
    def run_tests(self, test_labels, mock_save, extra_tests=None, **kwargs):
        mock_save.return_value = ImageFactory.get_image()
        return super().run_tests(test_labels, extra_tests=None, **kwargs)

Then I would run my tests using python manage.py tests --testrunner=runner.UnitTestRunner

---

Just for clarity the ImageFactory.get_image method is a custom method

from django.core.files.base import ContentFile
from factory.django import DjangoModelFactory
from io import BytesIO
from PIL import Image as PilImage
from random import randint

class ImageFactory(DjangoModelFactory):

    @classmethod
    def get_image(cls, name='trial', extension='png', size=None):
        if size is None:
            width = randint(20, 1000)
            height = randint(20, 1000)
            size = (width, height)

        color = (256, 0, 0)

        file_obj = BytesIO()
        image = PilImage.new("RGBA", size=size, color=color)
        image.save(file_obj, extension)
        file_obj.seek(0)
        return ContentFile(file_obj.read(), f'{name}.{extension}')