Avoid polluting an Objective-C implementation with builder-related code by "hiding" it in a category

GroupableItem+Builder.h

#import "GroupableItem.h"

@interface GroupableItemBuilder : NSObject

@property (nonatomic, strong) NSString *name;
@property (nonatomic, strong) NSString *groupingKey;
@property (nonatomic, assign) NSInteger second;
@property (nonatomic, assign) NSInteger minute;
@property (nonatomic, assign) NSInteger hour;
@property (nonatomic, assign) NSInteger day;
@property (nonatomic, assign) NSInteger month;
@property (nonatomic, assign) NSInteger year;

@end

@interface GroupableItem (Builder)

+ (GroupableItem *)itemWithBlock:(void (^)(GroupableItemBuilder *builder))block;

@end

GroupableItem+Builder.m

#import "GroupableItem+Builder.h"

@implementation GroupableItemBuilder

- (instancetype)init
{
    self = [super init];
    if (self) {
        _name = @"Default Name";
        _groupingKey = @"Default Grouping Property Value";
        _second = 0;
        _minute = 0;
        _hour = 6;
        _day = 25;
        _month = 4;
        _year = 1915;
    }
    return self;
}

@end

@implementation GroupableItem (Builder)

+ (GroupableItem *)itemWithBlock:(void (^)(GroupableItemBuilder *))block
{
    GroupableItemBuilder *builder = [[GroupableItemBuilder alloc] init];
    block(builder);

    GroupableItem *item = [[GroupableItem alloc] init];
    item.name = builder.name;
    item.groupingKey = builder.groupingKey;

    NSDateComponents *dateComponents = [[NSDateComponents alloc] init];
    dateComponents.second = builder.second;
    dateComponents.minute = builder.minute;
    dateComponents.hour = builder.hour;
    dateComponents.day = builder.day;
    dateComponents.month = builder.month;
    dateComponents.year = builder.year;
    item.date = [[[NSCalendar alloc] initWithCalendarIdentifier:NSGregorianCalendar] dateFromComponents:dateComponents];
    return item;
}

@end

GroupableItem.h

#import <Foundation/Foundation.h>

@interface GroupableItem : NSObject

@property (nonatomic, strong) NSString *name;
@property (nonatomic, strong) NSString *groupingKey;
@property (nonatomic, strong) NSDate *date;

@end

GroupableItem.m

#import "GroupableItem.h"

@implementation GroupableItem

@end

SomethingUsingGroupableItemTest.m

- (void)setUp
{
    [super setUp];

    //...

    self.items = @[

        [GroupableItem itemWithBlock:^(GroupableItemBuilder *builder) {
            builder.name = @"0";
            builder.hour = 9;
            builder.minute = 30;
        }],
        [GroupableItem itemWithBlock:^(GroupableItemBuilder *builder) {
            builder.name = @"1";
            builder.hour = 9;
            builder.minute = 30;
            builder.second = 1;
        }],

        [GroupableItem itemWithBlock:^(GroupableItemBuilder *builder) {
            builder.name = @"2";
            builder.hour = 10;
            builder.minute = 0;
        }],
        
        //...