New Test Case to Ensure PATCH Responses Are Correct

[mraineri]

There are some services that respond with 200 OK to PATCH requests, but their response body is either an error response with messages indicating "success", or simply the extended info messages arrays also indicating "success". Per the spec, 200 OK is supposed to contain the modified resource in response to a PATCH; the extended info array could be in there to convey warnings or properties that could not be modified, but that's an optional addition to the response.

[mraineri]

May be covered already with the test_patch_mixed_props test... Needs to be tested a bit...