As far as I can see, using Intellij 13.0.1, or a derived IDE, like RubyMine 6 Tab should work, with certain nuances.
When the focus is on the list of tests initially, I am able to tab between the list of tests and the console - the thing is, I cant see a cursor when I tab to the console/output, but if I use shift-up/down to I can see that the console definitely has the focus.
Pressing Tab again puts focus back to the list of tests on the left.
If the focus is in the console/output initially, pressing Tab has no effect and I have to use the mouse to 'escape'.
Earlier versions, based on ItelliJ 12 seem not to support this feature.
I hope this helps.