RestfulServerTest / JSONDataFormatterTest - Miscellaneous improvements

[sabina-talipova]

Description

The following can be made for RestfulServerTest:

• Test Relation getters
• Test filter and limit through GET params
• Test DELETE verb
• RestfulServerTest::testAuthenticatedGET:
  • create additional mock object with authenticated VIEW permissions. See
• RestfulServerTest::testGETRelationshipsXML & testGETRelationshipsXML:
  • Ratings should be set up by fixtures, doesn't work for some reason (See and here)

See: https://github.com/silverstripe/silverstripe-restfulserver/blob/23a7d78791e8e3ebb9aece0359dd91e34264c67e/tests/unit/RestfulServerTest.php#L27-L29