gistfile1.m

NSDictionary *testDict = [NSDictionary dictionary];
NSMutableDictionary *mutableTestDict = [NSMutableDictionary dictionary];

if ([testDict isKindOfClass:[NSDictionary class]]
    && ![testDict isKindOfClass:[NSMutableDictionary class]]  //notice the negation here!
    && [mutableTestDict isKindOfClass:[NSDictionary class]]
    && [mutableTestDict isKindOfClass:[NSMutableDictionary class]])
{
    NSLog(@"Hey Christian, klappt doch!");
}