A helper method that will tap one of the buttons programmatically.

UIAlertController.swift

// Source: http://stackoverflow.com/a/40634752/3400034
extension UIAlertController {
	func tapButton(at index: Int, animated: Bool) {
		guard Thread.isMainThread else {
			DispatchQueue.main.async {
				self.tapButton(at: index, animated: animated)
			}
			return
		}
		
		if (0 <= index) && (index < actions.count)
			, let block = actions[index].value(forKey: "handler")
		{
			typealias AlertHandler = @convention(block) (UIAlertAction) -> Void
			let blockPtr = UnsafeRawPointer(Unmanaged<AnyObject>.passUnretained(block as AnyObject).toOpaque())
			let handler = unsafeBitCast(blockPtr, to: AlertHandler.self)
			presentingViewController?.dismiss(animated: animated, completion: { [unowned self] in
				handler(self.actions[index])
			})
		}
	}
}

let alert = UIAlertController(title: "Hello", message: "world", preferredStyle: .alert)
alert.addAction(UIAlertAction(title: "OK", style: .cancel, handler: { (a: UIAlertAction) in
	print("tappedAction")
}))


alert.tapButton(at: 0, animated: false)