'we need to use a patched version of the get_deleted_objects so it works
with polymorphic models.
see filer.admin.patched.admin_utils.get_deleted_objects'

def test_can_delete_mixed_file_and_image_items(self):

    folder = Folder.objects.create(name='a    folder    with    files    and    images    inside')
    self.create_image(folder=folder, filename='i-am-a-image.jpg')
    self.create_file(folder=folder, filename='i-am-a-file.bin')
    self.assertEqual(Folder.objects.filter(id=folder.id).count(), 1)
    response = self.client.get(folder.get_admin_delete_url())
    self.assertEquals(response.status_code, 200)
    response = self.client.post(folder.get_admin_delete_url(), {'post': 'yes'})
    self.assertRedirects(response=response, expected_url=reverse('admin:filer-directory_listing-root'))
    self.assertEqual(Folder.objects.filter(id=folder.id).count(), 0)
