Create suite of test cases every media type should implement

[gregturn]

By having a suite of test cases based on the various models, ensure an adequate testing of each media type.

The various expectations would only require media types provide expected JSON files.

Would give media type implementers a good baseline for testing. Custom aspects of the media type could then be captured as extra tests.

[toedter]

That would be great! Once the infrastructure is set up I could contribute.