Swagger Accuracy Report should track/report coverage of response body properties

The Swagger Accuracy Report currently tracks coverage of operations and reports any operations that are not exercised in a test run. We want to extend coverage checking to properties of the response schema.

Optional properties of a response schema may not be returned for a particular test scenario and that means we cannot confirm that the property is correctly defined in terms of its name and type. So our confidence in the correctness of the API definition should take into account the coverage of response body properties achieved by the tests.

Start by locating the Swagger Accuracy Report implementation and its existing operation-coverage reporting, then trace how response schemas are inspected during a test run. Done means the report tracks which response-body properties are exercised and reports uncovered optional properties alongside existing operation coverage.

Written by the indexing model from the issue text.