Combo plan testing related

Hi 

Looking at a possible take over for DB/DC combo

DB has a safe harbor integrated formula but does not pass ratio test on its own (not sure about ABPT as I am not yet provided the testing. Top heavy provided under DB plan.

DC has deferral and 3% NESH and passes 410b ratio test. No PS allocation.

If both plans need to be aggregated for 410b testing, do they need to be tested for 401a4?

If you HAVE to aggregate to satisfy coverage then you must aggregate for nondiscrimination and then there are no safe harbors. If each plan has an otherwise safe harbor formula, if the DB can pass coverage by itself using average benefits, then you're OK.