SETUSER can be used by members of the sysadmin fixed server role to adopt the identity of another user in order to test the permissions of the other user.

Only use SETUSER with SQL Server users. It is not supported with Windows users. When SETUSER has been used to assume the identity of another user, any objects that are created are owned by the user being impersonated.

SETUSER remains in effect until another SETUSER statement is issued or until the current database is changed with the USE statement.