write (v3) tests that do (a lot) more for osullivan

[ndushay]

• tests that use the fixture objects?
• tests that ensure that given classes actually produce the desired json
  • abstract_resource (V3 abstract_resource beef up #19)
  • service (v3 service class: improve specificity, validation and tests #20)
  • manifest (V3 manifest: improve specificity, validation and tests #22- WIP)
  • sequence (v3 sequence: improve specificity, validation and tests #24 - WIP)
  • canvas (V3 canvas: improve specificity, validation and tests #25)
  • annotation_page (V3 annotation, annotationPage and choice object improvements #30)
  • annotation (V3 annotation, annotationPage and choice object improvements #30)
  • resource (V3 resource and image_resource tests improved #29)
  • image_resource (V3 resource and image_resource tests improved #29)
  • range
  • choice (V3 annotation, annotationPage and choice object improvements #30)
  • collection
  • annotation_collection

Chris's suggestion: borrow some code from purl to create a iiif presentation bits, and compare the created bits to expected bits.

Okay to add such tests only to v3 at this point, I would say.