admob iOS: To get test ads on this device, call: request.testDevices = @[ GAD_SIMULATOR_ID ];

This is an interesting error. What should I put in the GAD_SIMULATOR_ID slot? What does that mean exactly? Here's my code, directly from Google's Admob tutorial:

bannerView = [[GADBannerView alloc] initWithFrame:CGRectMake(self.view.frame.size.height, 0.0, GAD_SIZE_320x50.width, GAD_SIZE_320x50.height)];
bannerView.adUnitID = @"my adunitid";
bannerView.rootViewController = self;
[self.view addSubview:bannerView];
GADRequest *request = [GADRequest request];
request.testDevices = @[ GAD_SIMULATOR_ID ];
NSLog(@"%@", GAD_SIMULATOR_ID); //This returns "Simulator" if you were wondering
[bannerView loadRequest:request];