quick example of using block property to handle async unit tests for iOS. This assumes you're using SenTest

async-test.m

@property (nonatomic, copy) void (^testForCompletionBlock)(BOOL *testCompleted);

- (void)setUp {

    [super setUp];
  
    _testForCompletionBlock = ^(BOOL *testCompleted) {
      
      while (!*testCompleted) {
        
        NSDate *cycle = [NSDate dateWithTimeIntervalSinceNow:0.01];
        
        [[NSRunLoop currentRunLoop] runMode:NSDefaultRunLoopMode
                                 beforeDate:cycle];
      }
    };
}

- (void)test_Delete_All_Bar_Objects {
    @try {
      
      __block BOOL testCompleted = NO;

        NSFetchRequest *fetchRequest = [[NSFetchRequest alloc] init];
        NSEntityDescription *entity = [NSEntityDescription entityForName:@"Bar" inManagedObjectContext:_sm_open_Context];
        [fetchRequest setEntity:entity];
        [_sm_open_Context executeFetchRequest:fetchRequest onSuccess:^(NSArray *results) {
            for (id obj in results) {
                [_sm_open_Context deleteObject:obj];
                [_sm_open_Context saveOnSuccess:^{
                } onFailure:^(NSError *error) {
                    STAssertNil(error, @"There was an error! %@", error);
                }];
            }
          testCompleted = YES;
        } onFailure:^(NSError *error) {
          testCompleted = YES;
          STAssertNil(error, @"Error fetching! %@", error);
        }];
      
      _testForCompletionBlock(&testCompleted);

    } @catch (NSException * e) {
        NSLog(@"test_Delete_All_Bar_Objects failed: %@", [e description]);
    }
}