Demo of code executing even after a unit test has finished

async_test_crash_demo.m

- (void)setUp
{
  [super setUp];
  [MagicalRecord setupCoreDataStackWithInMemoryStore];
}

- (void)tearDown
{
  [MagicalRecord cleanUp]; // cleans up the CoreData stack to be ready for a clean state for the next tests
  // Note: any code after this line that would try to use CoreData will obviously fail 
  [super tearDown];
}

- (void)testFoo
{
  __block BOOL _done = NO;
  [self doSomeLongTaskWithCompletion:^{
    [[NSManagedObjectContext defaultContext] save:nil]; // Do some CoreData stuff here
    _done = YES;
   }];

  NSDate* timeoutDate = [NSDate dateWithTimeIntervalSinceNow:3];
  while (!_done && ([timeoutDate timeIntervalSinceNow]>0))
  {
    CFRunLoopRunInMode(kCFRunLoopDefaultMode, 0.01, YES);
  }

  STAssertTrue(_done, @"Test timed out");
}

- (void)doSomeLongTaskWithCompletion:(dispatch_block_t)completion
{
   // Some long task
   dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^{
     sleep(5); // imagine this is a long task
     completion();
   });
}



/* The problem:
 - The test will time out after 3 seconds, so before the "doSomeLonTaskWithCompletion:" method completes.
 - The test will then fail, and the -tearDown method will be called… cleaning the CoreData stack
 - But 2s later, the completion block will still be called, (even if the test is finised, the long method was still running) and  will call its CoreData stuff but the CoreData stack was already cleaned up by 'tearDown'! So this will crash.
*/