XCTest: Passing a function parameter

From XCTest file, I am calling a web service call and had put a wait block using "self.waitForExpectationsWithTimeout" API and to get the service response.

I have few test methods to be executed with this service response. When I store this response in a global variable and access it from other test function, this variable is coming as nil. What needs to be done here? Can I pass it as a function parameter?

Thanks