Refactor fixture generation for finder publisher spec.
Refactor fixture generation for finder publisher spec.

In preparation for adding new specs.

alphagov/specialist-publisher,alphagov/manuals-publisher,alphagov/specialist-publisher-rebuild,ministryofjustice/specialist-publisher,alphagov/specialist-publisher-rebuild,ministryofjustice/specialist-publisher,alphagov/manuals-publisher,alphagov/specialist-publisher-rebuild,ministryofjustice/specialist-publisher,alphagov/specialist-publisher,alphagov/manuals-publisher,ministryofjustice/specialist-publisher,alphagov/specialist-publisher,alphagov/specialist-publisher-rebuild