The first and most obvious way to tell if cookie dough is bad is to look for discoloration. The edges will be dark and will appear dry and crumbly. The inner dough will remain doughy, but the edges will have turned brown. This is a sign of oxidation. You may want to consider replacing the cookie dough with one that does not have eggs. Then you will know that you’re dealing with a bad batch.
Another sign that your dough is bad is the smell.