As a machine, the REST API should provide a list of Tests contained in a Test Plan's folder

The REST API should provide a GET operation for obtaining a list of Tests contained in a Test Plan's folder, along with their status.

 GET .../testplan/xxx/folder/yyy/tests

or by improving the current endpoint and passing a "folder" parameter specifying the folder's full path:

GET /rest/raven/1.0/api/testplan/{testPlanKey}/test?folder=regression