My son is 8 1/2 yrs old hhe has cough dry every night. i have got every test done, no use. what should i do?

Possible asthma: It sounds like this could be nocturnal asthma and/or allergy related as well. You should check bedroom and environment at home for dust and dust mites as well as mold. Also if you have pets keep them out of bedroom at least. See if your doctor can also get allergy test and treat empirically for possible asthma. If there is family history be especially suspicious.