CREATE TABLE [dbo].[test](
	[id] [int] IDENTITY( 1 , 1 ) NOT NULL
) ON [PRIMARY]

set identity_insert test on
insert into test (id) values( 1 )
set identity_insert test off

select * from test

use tempdb;
set nocount on;

if object_id('test') is not null
	drop table test;
create table test (a int identity( 1 , 1 ), b int);
go
insert into test (b) values( 1 )
go  10 
--
DBCC CHECKIDENT (test, RESEED,  0 );
go
--
insert into test (b) values( 2 )
go  10 

--There are duplicates
select COUNT(*) as [Num Of Duplicated Idenity Values], a
from test
group by a 
having COUNT(*) >  1 ;

select * from test order by a;

if object_id('test') is not null
	drop table test;