Unit test property has changed after dispatch_async using XCTest

What is the best way to unit test importantMainThreadStuffHasHappened is set to true after the dispatch_async in the code below?

class ViewController: UIViewController {

    var importantMainThreadStuffHasHappened = false

    override func viewDidLoad() {

        super.viewDidLoad()

        dispatch_async(dispatch_get_main_queue()) {
            self.importantMainThreadStuffHasHappened = true
        }
    }
}

This does not work since the dispatch_async code is executed after the XCTAssertTrue in the test.

func testimportantMainThreadStuffHasHappened() {

    let viewController = ViewController()
    _ = viewController.view
    XCTAssertTrue(viewController.importantMainThreadStuffHasHappened)
} 

I've heard two suggestions so far, both of which seem pretty outlandish:

1. Wrap dispatch_async in a helper so that the dispatch_async can be replaced in a mock like:

   protocol Dispatcher {
       func asyncMain(completion: dispatch_block_t)
   }
   
   struct Dispatch: Dispatcher {
       func asyncMain(completion: dispatch_block_t) {
           dispatch_async(dispatch_get_main_queue()) {
               completion()
           }
       }
   }
   
   struct MockDispatch: Dispatcher {
       func asyncMain(completion: dispatch_block_t) {
           completion()
       }
   }
   
   

2. Wait for the next run loop