How can a dentist test for a cracked tooth?

Lots of ways: Physical examination, x- rays, applying directed pressure, application of heat/cold. Not something you can determine at home. Please call your dentist for an evaluation and necessary treatment.

Cracked Tooth: It's not always easy for a dentist to tell if a tooth is cracked. More often than not, we test the teeth and good by the patient's symptoms which can lead us to say "You have cracked tooth syndrome." Sometimes we can see a crack in a tooth with X-rays (not very often though), we can transilluminate by shining light into the tooth to look for a crack, etc. Patient symptoms are the best indicator