The new job class blends code from the BackorderJob and the
CompleteBackorderJob for the specific case of adjusting quantities after
an order has been cancelled.
I would like to write a more general class which can be used for any
order amendmends but this was the quickest solution to cater for
currently running pilots.
- Add a fixture image to do the upload thanks to `fixture_file_upload`
- Check the response status, the content type and the response body for both logo image and promo image