CREATE LOGIN login1 WITH PASSWORD = 'J345#$)thb';
CREATE LOGIN login2 WITH PASSWORD = 'Uor80$23b';
GO
CREATE USER user1 FOR LOGIN login1;
CREATE USER user2 FOR LOGIN login2;
GO
begin tran t
GRANT IMPERSONATE ON USER:: user2 TO user1;
SELECT SUSER_NAME(), USER_NAME();
EXECUTE AS user = 'user2';
REVERT;

GRANT IMPERSONATE ON USER:: user1 TO user2;
SELECT SUSER_NAME(), USER_NAME();
EXECUTE AS user = 'user1';
revert;
rollback tran t