Currently, Wikibase REST API have a centralized test file for checking unsupported media type requests in repo/rest-api/tests/mocha/api-testing/UnsupportedMediaTypeTest.js.
We want to centralize the tests for the media types that the REST API supports.
For PATCH requests, it supports application/json and application/json-patch+json.
Wikibase REST API supports application/json for the remaining edit requests.