I would set up a test -maybe cover a wall with newspaper (because of the fine detail in the print) clamp the camera ona good solid tripod and shot some test shots with a remote cable on a slow fine grained film with a wide aperture (a shallow depth of field shows up focussing issues much better) Then swap the lens elements and repeat.

The trouble with putting a film through in 'normal' usage is that stopping down, camera shake and the fact that each image is different makes it difficult to spot subtle errors. Might be a long time before you hit the conditions that show up a focussing error.