No idea. What I might try -- assuming VisualWorks has an analogue for Squeak's Process class -- is to spin up a bunch of processes and have them compute factorials over and over or something. That should bog down the VW UI. 

Try asking at the address below, on the VisualWorks Non-Commercial mailing list. You'll get more folks who use VW there:

vwnc at cs.uiuc.edu

On Jul 11, 2013, at 1:20 PM, Fede <feferrara at gmx.net> wrote:

> Hi!
> I know this list is for squeak, sorry for the noise, maybe someone can help me with this. I´m looking for some tools (like HP LoadRunner) in order to perform a stress test to a VisualWorks 7.1 app client (with a Gemstone DB on the server side). I surfed the web for hours for nothing. Is there any tool on the market that can generate load on the VisualWorks GUI?
> 
> Thanks in advance.
> fef.-
>