my thoughts on testing:
once baby is on PROPER:
meds, dosing of meds, form of meds, combination of meds,
formula (alimentum/nutrimigen/neocate/elecare if necessary)/breastfeeding (diet if necessary)
and baby is still:
crying/fussy/unhappy most of the time, having terrible times w/ passing stools, forming stools, having foul smelling gas & stools
starting to have a feeding aversion
then I’d look into testing…but I would tackle meds & diet first…