External Class Extension Mimics Protected Members

ClassA.h

//
//  ClassA.h
//  TestHeader
//
//  Created by steve on 2015-04-29.
//  Copyright (c) 2015 steve. All rights reserved.
//

#import <Foundation/Foundation.h>

@interface ClassA : NSObject

@end

ClassA.m

//
//  ClassA.m
//  TestHeader
//
//  Created by steve on 2015-04-29.
//  Copyright (c) 2015 steve. All rights reserved.
//

#import "ClassA.h"
#import "Test.h"

@implementation ClassA

- (void)testWithMessage:(NSString *)message
{
    NSLog(@"%@", message);
}
@end

ClassB.h

//
//  ClassB.h
//  TestHeader
//
//  Created by steve on 2015-04-29.
//  Copyright (c) 2015 steve. All rights reserved.
//

#import "ClassA.h"

@interface ClassB : ClassA
- (void)doIt;
@end

ClassB.m

//
//  ClassB.m
//  TestHeader
//
//  Created by steve on 2015-04-29.
//  Copyright (c) 2015 steve. All rights reserved.
//

#import "ClassB.h"
#import "Test.h"

@implementation ClassB

- (void)doIt
{
    [self testWithMessage:@"My message"];
}
@end

main.m

//
//  main.m
//  TestHeader
//
//  Created by steve on 2015-04-29.
//  Copyright (c) 2015 steve. All rights reserved.
//

#import <Foundation/Foundation.h>
#import "ClassB.h"

int main(int argc, const char * argv[]) {
    @autoreleasepool {
        ClassB *classB = [ClassB new];
        [classB doIt];
    }
    return 0;
}

Test.h

//
//  Test.h
//  TestHeader
//
//  Created by steve on 2015-04-29.
//  Copyright (c) 2015 steve. All rights reserved.
//
#import <Foundation/Foundation.h>

@interface ClassA()
- (void)testWithMessage:(NSString *)message;
@end