Yes the Alter command to set to single_user did complete successfully. To ensure this I ran this code

USE [master]

ALTER DATABASE [TESTFULL] SET SINGLE_USER WITH ROLLBACK IMMEDIATE;

GO

and got this message

Msg 5064, Level 16, State 1, Line 2

Changes to the state or options of database 'TESTFULL' cannot be made at this time. The database is in single-user mode, and a user is currently connected to it.

Msg 5069, Level 16, State 1, Line 2

ALTER DATABASE statement failed.

Thanks

Kathy