Sql-server – ALTER DATABASE failed because a lock could not be placed on database ‘‘. Try again later

I really don't care what I do with this test database…it's for sandbox testing (attached to a production server instance)! All I'm trying to do is KILL all connections, drop and create test_db, if not asking for to much….and restore with some test data.

I've tried USE [MASTER] RESTORE DATABASE test_DB WITH RECOVERY GO , but got this error:

Msg 3101, Level 16, State 1, Line 1
Exclusive access could not be obtained because the database is in use.
Msg 3013, Level 16, State 1, Line 1
RESTORE DATABASE is terminating abnormally.

Also, tried
USE [master] ALTER DATABASE test_DB SET SINGLE_USER WITH ROLLBACK IMMEDIATE;, and got error:

Msg 5061, Level 16, State 1, Line 1
ALTER DATABASE failed because a lock could not be placed on database 'test_DB'. Try again later.

Msg 5069, Level 16, State 1, Line 1
ALTER DATABASE statement failed.

Also did
select min(spid) from master..sysprocesses where dbid = db_id('test_DB'), but my result set returned NULL

Below is my code:

 --- Kill Connections
    USE [master] 

    DECLARE @cmdKill VARCHAR(50)

    DECLARE killCursor CURSOR FOR
    SELECT 'KILL ' + Convert(VARCHAR(5), p.spid)
    FROM master.dbo.sysprocesses AS p
    WHERE p.dbid = db_id('test_DB')

    OPEN killCursor
    FETCH killCursor INTO @cmdKill

    WHILE 0 = @@fetch_status
    BEGIN
    EXECUTE (@cmdKill) 
    FETCH killCursor INTO @cmdKill
    END

    CLOSE killCursor
    DEALLOCATE killCursor 

    --Drop and Create 

    USE [master]
    GO

    IF  EXISTS (SELECT name FROM sys.databases WHERE name = N'test_DB')
    DROP DATABASE [test_DB]
    GO

    USE [master]
    GO


        CREATE DATABASE [test_DB] ON  PRIMARY 
        ( NAME = N'test_db_Data', FILENAME = N'\\some_place\d$\Program Files\Microsoft SQL Server\MSSQL10_50.MSSQLSERVER\MSSQL\DATA\test_DB.mdf' , SIZE = 125635136KB , MAXSIZE = UNLIMITED, FILEGROWTH = 20%)
         LOG ON 
        ( NAME = N'test_db_Log', FILENAME = N'E:\SQLLogs\test_DB.ldf' , SIZE = 1064320KB , MAXSIZE = UNLIMITED, FILEGROWTH = 20%)
        GO

    ALTER DATABASE [test_db] SET ....