Objective C - Unit testing dispatch_async block?

Question

I read other posts that come up with solutions to this question. However, their solutions require hacky code to be added to my application in order to be able to test it. To

Answer 1

Run the main loop briefly to let it call the async block:

- (void)testShouldFetchUserDataUsingCorrectId {
   static NSString *userId = @"sdfsdfsdfsdf";
   self.viewController.userId = userId;
   self.viewController.serviceClient = [[OCMockObject niceMockForClass:[ServiceClient class]];

   [[(OCMockObject *)self.viewController.serviceClient expect] fetchDataForUserId:userId];
   [self.viewController view];
   [[NSRunLoop mainRunLoop] runUntilDate:[NSDate dateWithTimeIntervalSinceNow:0.01]];
   [(OCMockObject *)self.viewController.serviceClient verify];
}

I suppose this could fail on a heavily-loaded system, or if you have a bunch of other stuff (timers or other blocks) going on the main thread. If that's the case, you need to run the run loop longer (which slows down your test case), or run it repeatedly until the mock object's expectations have been met or a timeout is reached (which requires adding a method to the mock object to query whether its expectations have been met).