As far as O'Sullivan is concerned it's an ideal game for such an exercise.
Opportunity beckons for Geordan Murphy who has been named at full-back. In the past, this hugely gifted player, hasn't managed to transfer his club form to international level, and with O'Sullivan looking for back-up to Girvan Dempsey, Murphy needs a big game on Sunday.
But it's in the pack, that the fiercest competition for RWC places lies and Marcus Horan, Frank Sheahan, Leo Cullen, Alan Quinlan, Kieron Dawson and replacements, Eric Miller and Mick O'Driscoll will be only too aware that Sunday's test is exactly that. Miller is troubled by a hamstring strain and Victor Costello has been called into the squad as cover.
Ireland. G Murphy; S Horgan, B O'Driscoll capt, K Maggs, J Bishop; D Humphreys, G Easterby; M Horan, F Sheahan, J Hayes; L Cullen. M O'Kelly; A Quinlan, K Dawson, A Foley.Replacements: S Byrne, R Corrigan, M O'Driscoll, E Miller, P Stringer, R O'Gara, G D'Arcy.