@interface PIPObjectForTests : PIPObject
{
    NSMutableSet * pipos_;
}
@property NSMutableSet * pipos;
@end

-------------------------------
#import "PIPObjectForTests.h"

@implementation PIPObjectForTests
@synthesize pipos = pipos_;


@end

-----------------------------------

PIPObjectForTests *o = [PIPObjectForTests create];
    [o pipos];
    [o countOfPipos];
    [o addPipos:o2];

No visible @interface for 'PIPObjectForTests' declares the selector 'countOfPipos'
No visible @interface for 'PIPObjectForTests' declares the selector 'addPipos:'