Fork your tests with IntelliJ IDEA 10.5 EAP build 106.447
One of the latest features was long awaited fork mode for JUnit run configurations. Since now it is possible to run your tests in separate VMs. It is possible to choose to fork on class level only.
Check out the list of all changes in the release notes on the IntelliJ IDEA EAP page and download the new build.
Btw, we are going to freeze IDEA 10.5 development soon, so we are actively looking forward for your feedback!