I am automating web-application tests that are driven by Selenium architecture in Windows VMs, connecting via Windows Remote Desktop. It became known to me that Flash/SWF and other in-browser elements behave differently if the VM window is opened/shown (all is cool) and when the window is closed (or maybe even minimized). Which means that browsers/plugins engage some optimization if no one watches the screen (I might be wrong with that – if so – please correct me).
As a (working) workaround, installing VNC (and logging into it at least once before running the tests) helps. From that moment noone needs to "watch" the monitor.
I think that the same functionality/system calls is used by (for example) movie players that cancel the screensaver during the film watching.
The question is if any special daemon was written for those purposes, so I won’t need to connect to those machines by VNC, but only to run the daemon.
Update: http://www.jddesign.co.uk/products/freeware/freeware_programs.htm – meanwhile found this utility, checking if it will do the job. Advices are still welcomed.
Update N2: the utility above doesn’t do the job.
What you experience is the standard render optimization: The OS will ignore all rendering commands if the window isn’t visible.
My guess is that VM tools “minimize” the whole desktop to save memory as long as no one is connected.
On Unix, I’d write a small script which runs the VNC viewer when the tests are started.
[EDIT] What you’re looking for is a kind of /dev/null device for VNC connections.
Here is a solution that might work: Download the sources for the TightVNC Java Viewer (license: GPL) and remove all the rendering code.
That should allow you to start a headless VNC client for your tests.