Shows that CFMutableSetRef doesn't transfer CFSetCallBacks to NSSet returned from setByAddingObject:

NSCFMutableSetWithOpaquePointersTests.m

#define HJBAssertNotSame(expression1, expression2, ...) \
XCTAssert((expression1) != (expression2), \
__VA_ARGS__)

- (void)testCFMutableSetWithOpaquePointersCopiedToNSSetByAddingDoesNotKeepOpaquePointerBehavior
{
    NSString * _Nonnull string1 = [@"ab" stringByAppendingString:@"cd"];
    NSString * _Nonnull string2 = [@"a" stringByAppendingString:@"bcd"];
    
    TWAssertNotSame(string1,
                    string2);
    
    NSMutableSet<NSString *> * _Nonnull stringsMutableSet = (NSMutableSet * _Nonnull) CFBridgingRelease(CFSetCreateMutable(NULL,
                                                                                                                           0,
                                                                                                                           NULL));
    [stringsMutableSet addObject:string1];
    [stringsMutableSet addObject:string2];
    
    XCTAssertEqual(stringsMutableSet.count,
                   (NSUInteger) 2);
    
    NSString * _Nonnull string3 = [@"abc" stringByAppendingString:@"d"];
    
    HJBAssertNotSame(string1,
                    string3);
    HJBAssertNotSame(string2,
                    string3);
    
    NSSet<NSString *> * _Nonnull stringsSetCopiedFromStringsMutableSet = [stringsMutableSet setByAddingObject:string3];
    
    XCTAssertEqual(stringsSetCopiedFromStringsMutableSet.count,
                   (NSUInteger) 1);
}