Добавление метода "renameKey:to:" к NSMutableDisctionary и тесты для него при помощи kiwi

NSMutableDictionary+Utils.h

#import <Foundation/Foundation.h>

@interface NSMutableDictionary (Utils)
- (void)renameKey:(NSString *)oldKeyName to:(NSString *)newKeyName;
@end

NSMutableDictionary+Utils.m

#import "NSMutableDictionary+Utils.h"

@implementation NSMutableDictionary (Utils)
- (void)renameKey:(NSString *)oldKeyName to:(NSString *)newKeyName {
    [self setValue:[self valueForKey:oldKeyName] forKey:newKeyName];
    [self removeObjectForKey:oldKeyName];
}
@end

NSMutableDictionaryUtilsSpec.m

#import "Kiwi.h"
#import "NSMutableDictionary+Utils.h"

SPEC_BEGIN(NSMutableDictionaryUtilsSpec)

describe(@"NSMutableDictionary", ^{
    __block NSMutableDictionary *subject = nil;
    static NSString *oldKey = @"oldKey";
    static NSString *newKey = @"newKey";
    __block id valueForOldKey = nil;

    beforeEach(^{
        subject = [NSMutableDictionary dictionaryWithObject:@"my object" forKey:oldKey];
        valueForOldKey = [subject valueForKey:oldKey];
    });

    context(@"before rename", ^{
        it(@"should have value for old key", ^{
            [[[subject valueForKey:oldKey] should] beIdenticalTo:valueForOldKey];
        });

        it(@"should not have newKey", ^{
            [[subject valueForKey:newKey] shouldBeNil];
        });
    });

    context(@"after rename", ^{
        beforeEach(^{
            [subject renameKey:oldKey to:newKey];
        });

        it(@"should have appropriate value for new key", ^{
            [[[subject valueForKey:newKey] should] beIdenticalTo:valueForOldKey];
        });

        it(@"should not have any value for old key", ^{
            [[subject valueForKey:oldKey] shouldBeNil];
        });
    });
});

SPEC_END