How will a doctor test for cataracts during routine exam?

With a complete exam. Your doc will first ask a series of questions: how bad do you feel your vision is, does it stop you from doing things you enjoy, etc. They he/she will do a dilated exam and look at your lens. If the lens looks dark enough and you're having trouble, cataract surgery will be recommended.
Cataract. The ophthalmologist will use a slit lamp to magnify the front of the eye to look for cataracts.
Yes. Cataract cause: Cataract occur from change in lens proteins which cause whitening/clouding/opacity of clear lens composition: can be due to an infection or inflammation from birth/congential (ie, rubella), old age/genetics, steroid use, trauma, poor diet; smoking & Diabetes increases risk. Can be seen on microscope (slit lamp) exam easily. More info: eyedoc2020@blogspot.com.