How to "stop" a service?

[Yee-Kang Chang]

I'm trying to test ServiceUnavailableException (as part of vtest) -- to 
simulate that a service is unavailable and the Exception will be thrown. 
The current idea is to have a service "started", invoke some operation, 
"stop" it, and then invoke some other operation to see if a 
ServiceUnavailableException will be thrown.  Is there a way for us to 
"stop" a service in Tuscany?

Or, there's better ways for us to "test" ServiceUnavailableException?

Thank you!