NSManagedObjectContextDidChangeNotification not being called in gh-unit

[luhui]

I just write a test case for core data observer, but I found the NSManagedObjectContextDidChangeNotification not called with update the value, but It is called in my application with the same code.
My test code below:

    [MagicalRecord setupAutoMigratingCoreDataStack];
    [[NSNotificationCenter defaultCenter] addObserverForName:NSManagedObjectContextObjectsDidChangeNotification object:[NSManagedObjectContext MR_defaultContext] queue:[NSOperationQueue mainQueue] usingBlock:^(NSNotification *note) {
        NSLog(@"did change:%@", note);
    }];
    [MagicalRecord saveWithBlockAndWait:^(NSManagedObjectContext *localContext) {
        Babies *b = [Babies MR_createInContext:localContext];
        b.nickName = @"aloha";
        b.objectId = @"1";
    }];
    Babies *b = [Babies MR_findFirstByAttribute:BaseEntityAttributes.objectId withValue:@"1" inContext:[NSManagedObjectContext MR_defaultContext]];
    NSLog(@"b:%@ context:%@", b.nickName, [[b managedObjectContext] MR_parentChain]);
    [MagicalRecord saveWithBlockAndWait:^(NSManagedObjectContext *localContext) {
        Babies *e = [b MR_inContext:localContext];
        e.nickName = @"cool";
    }];
    NSLog(@"b:%@", b.nickName);

dependence with MagicalReocrd

The first 'saveWithBlockAndWait:' will insert an entity, the NSManagedObjectContextDidChangeNotification is called.

The second saveWithBlockAndWait: will update the entity has inserted above, and NSManagedObjectContextDidChangeNotification is not being called, but the entity has already refresh.

Any idea to resolve this problem?