We need to add tests for the following:
- CustomManager.delete deletes all photos in self.get_queryset().
- Photo.delete deletes the image from the file system.
- Photo.delete does not throw an exception when there is no image.
- Photo.save deletes the old image from the file system when being replaced with a new one (can be None).
- Photo.save does not throw an exception when there is no old image.
We need to add tests for the following: