I can see JoeV point but the only real test is what patterned wall paper looks like.
An out of focus christmas tree or set of streetlights can show how the boketh abberation varies accross the frame, but this is a secondary test, if you can shave with the in focus at f2 I'd not worry as much. You have seem Jorges shots of focus errors with his modern aspherics?
For the last 13 months I've only used a Kiev (or Contax), apart from folders, Fed's, Zorki's, M2, etc.,... and a digital to record dismantle sequences...