You are not allowed to have severe windshield cracks. I personally don't feel 1 Crack is severe but I would suggest getting it replaced as soon as possible. I know the weather changing makes it very easy to get cracks and they never happen at an opportune time. I don't see anything specific about how bad a crack can be before failing tech. Best I can say is bring it and we can evaluate there but ultimately the safety steward has ruling over all.