Use JsonPath to test Json responses
Changed configuration to enable XML based responses

Having content negotiation with more than just JSON content
might follow REST principles.

All entities annotated with e.g. @XmlRootElement can be send as XML data.
This requires client to send Accept header with value "application/json"
to fetch JSON responses.
Default Accept header send by client is something like:
"text/html,application/xhtml+xml,application/xml"
which requests an XML document, not JSON document but JSON is expected.
Check result media type in controller tests