With Xcode 7 Beta 4, Apple gave us a way to wait asynchronously during UI tests. This gist lets you wait on an Activity Indicator to finish.

UITestExtension.swift

import Foundation
import XCTest

extension XCTestCase {

    func waitForActivityIndicatorToStartAndFinishSpinning(activityIndicatorElement: XCUIElement, timeout: NSTimeInterval = 30.0) {
        let inProgressPredicate = NSPredicate(format: "label = 'In progress'")
        self.expectationForPredicate(inProgressPredicate, evaluatedWithObject: activityIndicatorElement, handler: nil)
        self.waitForExpectationsWithTimeout(timeout, handler: nil)
        
        let progressHaltedPredicate = NSPredicate(format: "label = 'Progress halted'")
        self.expectationForPredicate(progressHaltedPredicate, evaluatedWithObject: activityIndicatorElement, handler: nil)
        self.waitForExpectationsWithTimeout(timeout, handler: nil)
    }
}