Wagtail tests, creating image file to match JSON fixtures

tests.py

from wagtail.tests.utils import WagtailPageTests

import os
import PIL.Image
from django.core.files.images import ImageFile
from wagtail.images import get_image_model
Image = get_image_model()

def make_test_image_file(filename='hero.jpg', colour='white', size=(960, 450)):
    if os.access(filename, os.R_OK):
        return ImageFile(filename)

    ext = os.path.splitext(filename)[1].lower()
    if ext == '.jpg' or ext == '.jpeg':
        image_type = ('RGB', 'JPEG')
    elif ext == '.png':
        image_type = ('RGBA', 'PNG')
    else:
        raise ValueError("Cannot determine intended image type for %s" % filename)

    image = PIL.Image.new(image_type[0], size, colour)
    image.save(filename, image_type[1])
    return ImageFile(filename)


class ImageFixturesMixin:
    def setUp(self):
        super(ImageFixturesMixin, self).setUp()

        for img in Image.objects.all():
            make_test_image_file(
                filename=settings.MEDIA_ROOT + img.file.name,
                size=(img.width, img.height),
                colour="black",
            )

            
class HomePageTests(ImageFixturesMixin, WagtailPageTests):
    fixtures = ["test_base.json"]

    def test_empty_home_page(self):
        # implement tests here...