How to use the API to get all Test Cases of a Test Folder?
To receive all the Test Cases of a given Test Folder:
You need to know the ObjectID of that Test Folder. You can query the Test Folder endpoint to retrieve it.
Then, issue a Get call to the collection of Test Cases on the Test Folder endpoint. Here is how it's done:
https://rally1.rallydev.com/slm/webservice/v2.0/TestFolder/<TestFolder_ObjectID>/TestCases
This call will return the collection of Test Cases, then you can use that collection to query further and find a particular test case.