If you have do this repeatedly over a long time, I suggest you take a look at BOINC.
Quoting from here: "BOINC is designed to be a free structure for anyone wishing to start a distributed computing project."
You would use the BOINC API and you will have to set up a server.
There are several people who have used BOINC for their own projects: example 1, example 2, example 3.
Note that BOINC is especially suited for CPU-intensive processes. If your test processes are light on CPU but heavy on disk or memory, BOINC may not be suited.