Implement Test Cases for FHIR Encounter Endpoint API

Implement Test Cases for the FHIR Encounter Endpoint, allowing to automatically test whether API calls yield expected results when supplying Encounter Resources to Mainzelliste. Each Encounter needs to contain some kind of reference to a Patient itself.

A test case includes:

• a FHIR Resource that is send to the endpoint
• checking the response (i.e. check the return HTTP Status Code, check the response content, ..)
• optional: follow-up check in the database or with a subsequent API request (i.e. GET a previously POSTed Encounter Resource)

Include success cases as well as error cases (e.g. expect a graceful error on sending an empty request-body)